Chemistry and Chemical Reactivity

John C. Kotz, Paul M. Treichel, John R. Townsend

Chapter 5

Principles of Chemical Reactivity: Energy and Chemical Reactions - all with Video Answers

Educators

Chapter Questions

Problem 1

The flashlight in the photo does not use batteries. Instead, you move a lever, which turns a geared mechanism and results finally in light from the bulb. What type of energy is used to move the lever? What type or types of energy are produced?
PICTURE CANT COPY

Alice .

Alice .

Numerade Educator

Problem 2

A solar panel is pictured in the photo. When light shines on the panel, it generates an electric current that is used by a small electric motor to propel the car. What types of energy are involved in this setup?
PICTURE CANT COPY

Adam Wade

Numerade Educator

Problem 3

You are on a diet that calls for eating no more than 1200 Cal/day. What is this energy in joules?

Vysakh M

Numerade Educator

Problem 4

A 2 -in. piece of chocolate cake with frosting provides $1670 \mathrm{kJ}$ of energy. What is this in dietary Calories (Cal)?

Pronoy Sinha

Numerade Educator

Problem 5

One food product has an energy content of $170 \mathrm{kcal}$ per serving, and another has $280 \mathrm{kJ}$ per serving. Which food provides the greater energy per serving?

Lottie Adams

Numerade Educator

Problem 6

Which provides the greater energy per serving, a raw apple or a raw apricot? Go to the USDA Nutrient Database on the World Wide Web for the information:
http://www.ars.usda.gov/main/site_main. htm?modecode $=12354500 .$ Report the energy content of the fruit in $\mathrm{k}$ cal and $\mathrm{k} \mathrm{J}$.

Banhishikha Sinha

Banhishikha Sinha

Numerade Educator

Problem 7

The molar heat capacity of mercury is $28.1 \mathrm{J} / \mathrm{mol} \cdot \mathrm{K}$ What is the specific heat capacity of this metal in $\mathrm{J} / \mathrm{g} \cdot \mathrm{K}$ ?

Alice .

Numerade Educator

Problem 8

The specific heat capacity of benzene $\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)$ is $1.74 \mathrm{J} / \mathrm{g} \cdot \mathrm{K}$. What is its molar heat capacity (in $J / m o l \cdot K) ?$

Adam Wade

Numerade Educator

Problem 9

The specific heat capacity of copper is $0.385 \mathrm{J} / \mathrm{g} \cdot \mathrm{K}$ How much energy is required to heat 168 g of copper from $-12.2^{\circ} \mathrm{C}$ to $+25.6^{\circ} \mathrm{C} ?$

Breanna Kloczkowski

Breanna Kloczkowski

Numerade Educator

Problem 10

How much energy is required to raise the temperature of $50.00 \mathrm{mL}$ of water from $25.52^{\circ} \mathrm{C}$ to $28.75^{\circ} \mathrm{C} ?$ (The density of water at this temperature is $0.997 \mathrm{g} / \mathrm{mL} .)$

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 11

The initial temperature of a $344-\mathrm{g}$ sample of iron is $18.2^{\circ} \mathrm{C} .$ If the sample absorbs $2.25 \mathrm{kJ}$ of energy as heat, what is its final temperature?

Bin Chen

Numerade Educator

Problem 12

After absorbing $1.850 \mathrm{kJ}$ of energy as heat, the temperature of a $0.500-\mathrm{kg}$ block of copper is $37^{\circ} \mathrm{C} .$ What was its initial temperature?

Bin Chen

Numerade Educator

Problem 13

A 45.5 -g sample of copper at $99.8^{\circ} \mathrm{C}$ is dropped into a beaker containing $152 \mathrm{g}$ of water at $18.5^{\circ} \mathrm{C} .$ What is the final temperature when thermal equilibrium is reached?

Alice .

Numerade Educator

Problem 14

A 182 -g sample of gold at some temperature is added to $22.1 \mathrm{g}$ of water. The initial water temperature is $25.0^{\circ} \mathrm{C},$ and the final temperature is $27.5^{\circ} \mathrm{C} .$ If the specific heat capacity of gold is $0.128 \mathrm{J} / \mathrm{g} \cdot \mathrm{K},$ what was the initial temperature of the gold?

Adam Wade

Numerade Educator

Problem 15

One beaker contains 156 g of water at $22^{\circ} \mathrm{C},$ and a second beaker contains $85.2 \mathrm{g}$ of water at $95^{\circ} \mathrm{C} .$ The water in the two beakers is mixed. What is the final water temperature?

Alice .

Numerade Educator

Problem 16

When 108 g of water at a temperature of $22.5^{\circ} \mathrm{C}$ is mixed with $65.1 \mathrm{g}$ of water at an unknown temperature, the final temperature of the resulting mixture is $47.9^{\circ} \mathrm{C} .$ What was the initial temperature of the second sample of water?

Adam Wade

Numerade Educator

Problem 17

A 13.8 g piece of zinc was heated to $98.8^{\circ} \mathrm{C}$ in boiling water and then dropped into a beaker containing 45.0g of water at $25.0^{\circ} \mathrm{C}$. When the water and metal come to thermal equilibrium, the temperature is $27.1^{\circ} \mathrm{C}$ What is the specific heat capacity of zinc?

Alice .

Numerade Educator

Problem 18

A 237 -g piece of molybdenum, initially at $100.0^{\circ} \mathrm{C},$ is dropped into $244 \mathrm{g}$ of water at $10.0^{\circ} \mathrm{C} .$ When the system comes to thermal equilibrium, the temperature is $15.3^{\circ} \mathrm{C} .$ What is the specific heat capacity of molybdenum?

Adam Wade

Numerade Educator

Problem 19

How much energy is evolved when 1.0 L of water at
$0^{\circ} \mathrm{C}$ solidifies to ice? (The heat of fusion of water is $333 \mathrm{J} / \mathrm{g} .)$

Himanshu Garg

Numerade Educator

Problem 20

The energy required to melt $1.00 \mathrm{g}$ of ice at $0^{\circ} \mathrm{C}$ is $333 \mathrm{J} .$ If one ice cube has a mass of $62.0 \mathrm{g}$ and a tray contains 16 ice cubes, what quantity of energy is $\mathrm{re}$ quired to melt a tray of ice cubes to form liquid water at $0^{\circ} \mathrm{C} ?$

David Collins

Numerade Educator

Problem 21

How much energy is required to vaporize $125 \mathrm{g}$ of benzene, $\mathrm{C}_{6} \mathrm{H}_{6},$ at its boiling point, $80.1^{\circ} \mathrm{C} ?$ (The heat of vaporization of benzene is $30.8 \mathrm{kJ} / \mathrm{mol} .$ )

Bin Chen

Numerade Educator

Problem 22

Chloromethane, $\mathrm{CH}_{3} \mathrm{Cl}$, arises from microbial fermentation and is found throughout the environment. It is also produced industrially and is used in the manufacture of various chemicals and has been used as a topical anesthetic. How much energy is required to convert $92.5 \mathrm{g}$ of liquid to a vapor at its boiling point, $-24.09^{\circ} \mathrm{C} ?$ (The heat of vaporization of $\mathrm{CH}_{3} \mathrm{Cl}$ is 21.40 $\mathrm{kJ} / \mathrm{mol} .)$

Bin Chen

Numerade Educator

Problem 23

The freezing point of mercury is $-38.8^{\circ} \mathrm{C} .$ What quantity of energy, in joules, is released to the surroundings if $1.00 \mathrm{mL}$ of mercury is cooled from $23.0^{\circ} \mathrm{C}$ to -38.8
$^{\circ} \mathrm{C}$ and then frozen to a solid? (The density of liquid mercury is $13.6 \mathrm{g} / \mathrm{cm}^{3} .$ Its specific heat capacity is 0.140 $\mathrm{J} / \mathrm{g} \cdot \mathrm{K} \text { and its heat of fusion is } 11.4 \mathrm{J} / \mathrm{g} .)$

Alice .

Numerade Educator

Problem 24

What quantity of energy, in joules, is required to raise the temperature of $454 \mathrm{g}$ of tin from room temperature, $25.0^{\circ} \mathrm{C},$ to its melting point, $231.9^{\circ} \mathrm{C},$ and then melt the tin at that temperature? (The specific heat capacity of tin is $0.227 \mathrm{J} / \mathrm{g} \cdot \mathrm{K},$ and the heat of $\mathrm{fu}$ sion of this metal is $59.2 \mathrm{J} / \mathrm{g} .$ )

Nishant Kumar

Numerade Educator

Problem 25

Ethanol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH},$ boils at $78.29^{\circ} \mathrm{C} .$ How much energy, in joules, is required to raise the temperature of $1.00 \mathrm{kg}$ of ethanol from $20.0^{\circ} \mathrm{C}$ to the boiling point and then to change the liquid to vapor at that temperature? (The specific heat capacity of liquid ethanol is $2.44 \mathrm{J} / \mathrm{g} \cdot \mathrm{K},$ and its enthalpy of vaporization is $855 \mathrm{J} / \mathrm{g} .)$

Bin Chen

Numerade Educator

Problem 26

A 25.0 -mL sample of benzene at $19.9^{\circ} \mathrm{C}$ was cooled to its melting point, $5.5^{\circ} \mathrm{C},$ and then frozen. How much energy as heat was given off in this process? (The density of benzene is $0.80 \mathrm{g} / \mathrm{mL} ;$ its specific heat capacity is $1.74 \mathrm{J} / \mathrm{g} \cdot \mathrm{K},$ and its heat of fusion is $127 \mathrm{J} / \mathrm{g} .$ )

Jennifer Hudspeth

Jennifer Hudspeth

Numerade Educator

Problem 27

Nitrogen monoxide, a gas recently found to be involved in a wide range of biological processes, reacts with oxygen to give brown $\mathrm{NO}_{2}$ gas.
$$\begin{aligned}
2 \mathrm{NO}(\mathrm{g})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{NO}_{2}(\mathrm{g}) & \\
\Delta_{\mathrm{r}} H^{\circ}=&-114.1 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}
\end{aligned}$$
Is this reaction endothermic or exothermic? What is the enthalpy change if $1.25 \mathrm{g}$ of $\mathrm{NO}$ is converted completely to $\mathrm{NO}_{2} ?$

Ronald Prasad

Numerade Educator

Problem 28

Calcium carbide, $\mathrm{CaC}_{2}$, is manufactured by the reaction of CaO with carbon at a high temperature. (Calcium carbide is then used to make acetylene.) $\mathrm{CaO}(\mathrm{s})+3 \mathrm{C}(\mathrm{s}) \rightarrow \mathrm{CaC}_{2}(\mathrm{s})+\mathrm{CO}(\mathrm{g})$
$$\Delta_{\mathrm{r}} H^{\circ}=+464.8 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}$$
Is this reaction endothermic or exothermic? What is the enthalpy change if $10.0 \mathrm{g}$ of $\mathrm{CaO}$ is allowed to react with an excess of carbon?

Bin Chen

Numerade Educator

Problem 29

Isooctane $(2,2,4$ -trimethylpentane), one of the many hydrocarbons that make up gasoline, burns in air to give water and carbon dioxide.
$$\begin{aligned}
2 \mathrm{C}_{8} \mathrm{H}_{18}(\ell)+25 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 16 \mathrm{CO}_{2}(\mathrm{g})+18 \mathrm{H}_{2} \mathrm{O}(\ell) \\
\Delta_{r} H^{\circ}=-10,922 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}
\end{aligned}$$What is the enthalpy change if you burn $1.00 \mathrm{L}$ ofisooctane(density$=0.69\mathrm{g}/\mathrm{mL}) ?$

Lottie Adams

Numerade Educator

Problem 30

Acetic acid, $\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}$, is made industrially by the reaction of methanol and carbon monoxide.
$\mathrm{CH}_{3} \mathrm{OH}(\ell)+\mathrm{CO}(\mathrm{g}) \rightarrow \mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}(\ell)$
$$\Delta_{r} H^{\circ}=-355.9 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}$$
If you produce $1.00 \mathrm{L}$ of acetic acid $(d=1.044 \mathrm{g} / \mathrm{mL})$ by this reaction, how much energy as heat is evolved?

Adam Wade

Numerade Educator

Problem 31

Assume you mix $100.0 \mathrm{mL}$ of $0.200 \mathrm{M} \mathrm{CsOH}$ with $50.0 \mathrm{mL}$ of $0.400 \mathrm{M} \mathrm{HCl}$ in a coffee-cup calorimeter. The following reaction occurs:
$$\mathrm{CsOH}(\mathrm{aq})+\mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{CsCl}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell)$$
The temperature of both solutions before mixing was $22.50^{\circ} \mathrm{C},$ and it rises to $24.28^{\circ} \mathrm{C}$ after the acid-base reaction. What is the enthalpy change for the reaction per mole of CsOH? Assume the densities of the solutions are all $1.00 \mathrm{g} / \mathrm{mL}$ and the specific heat capacities of the solutions are $4.2 \mathrm{J} / \mathrm{g} \cdot \mathrm{K}$

Alice .

Numerade Educator

Problem 32

You mix $125 \mathrm{mL}$ of $0.250 \mathrm{M} \mathrm{CsOH}$ with $50.0 \mathrm{mL}$ of $0.625 \mathrm{M} \mathrm{HF}$ in a coffee-cup calorimeter, and the temperature of both solutions rises from $21.50^{\circ} \mathrm{C}$ before mixing to $24.40^{\circ} \mathrm{C}$ after the reaction.
$$\mathrm{CsOH}(\mathrm{aq})+\mathrm{HF}(\mathrm{aq}) \rightarrow \mathrm{CsF}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell)$$
What is the enthalpy of reaction per mole of $\mathrm{CsOH} ?$ Assume the densities of the solutions are all $1.00 \mathrm{g} / \mathrm{mL}$ and the specific heats of the solutions are $4.2 \mathrm{J} / \mathrm{g} \cdot \mathrm{K}$

Adam Wade

Numerade Educator

Problem 33

A piece of titanium metal with a mass of $20.8 \mathrm{g}$ is heated in boiling water to $99.5^{\circ} \mathrm{C}$ and then dropped into a coffee-cup calorimeter containing $75.0 \mathrm{g}$ of water at $21.7^{\circ} \mathrm{C} .$ When thermal equilibrium is reached, the final temperature is $24.3^{\circ} \mathrm{C} .$ Calculate the specific heat capacity of titanium.

Alice .

Numerade Educator

Problem 34

A piece of chromium metal with a mass of $24.26 \mathrm{g}$ is heated in boiling water to $98.3^{\circ} \mathrm{C}$ and then dropped into a coffee-cup calorimeter containing $82.3 \mathrm{g}$ of water at $23 . \overline{3}^{\circ} \mathrm{C} .$ When thermal equilibrium is reached, the final temperature is $25.6^{\circ} \mathrm{C} .$ Calculate the specific heat capacity of chromium.

Adam Wade

Numerade Educator

Problem 35

Adding $5.44 \mathrm{g}$ of $\mathrm{NH}_{4} \mathrm{NO}_{3}(\mathrm{s})$ to $150.0 \mathrm{g}$ of water in a coffee-cup calorimeter (with stirring to dissolve the salt) resulted in a decrease in temperature from $18.6^{\circ} \mathrm{C}$ to $16.2^{\circ} \mathrm{C} .$ Calculate the enthalpy change for dissolving $\mathrm{NH}_{4} \mathrm{NO}_{3}(\mathrm{s})$ in water, in $\mathrm{kJ} / \mathrm{mol}$. Assume that the solution (whose mass is $155.4 \mathrm{g}$ ) has a specific heat capacity of $4.2 \mathrm{J} / \mathrm{g} \cdot \mathrm{K}$. (Cold packs take advantage of the fact that dissolving ammonium nitrate in water is an endothermic process.)
PICTURE CANT COPY

Amany Waheeb

Numerade Educator

Problem 36

You should use care when dissolving $\mathrm{H}_{2} \mathrm{SO}_{4}$ in water because the process is highly exothermic. To measure the enthalpy change, $5.2 \mathrm{g} \mathrm{H}_{2} \mathrm{SO}_{4}(\ell)$ was added (with stirring) to 135 g of water in a coffee-cup calorimeter. This resulted in an increase in temperature from $20.2^{\circ} \mathrm{C}$ to $28.8^{\circ} \mathrm{C} .$ Calculate the enthalpy change for the process $\mathrm{H}_{2} \mathrm{SO}_{4}(\ell) \rightarrow \mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}),$ in $\mathrm{kJ} / \mathrm{mol}$

Adam Wade

Numerade Educator

Problem 37

Sulfur $(2.56 \mathrm{g})$ is burned in a constant volume calorimeter with excess $\mathrm{O}_{2}(\mathrm{g}) .$ The temperature increases from $21.25^{\circ} \mathrm{C}$ to $26.72^{\circ} \mathrm{C} .$ The bomb has a heat capacity of $923 \mathrm{J} / \mathrm{K},$ and the calorimeter contains $815 \mathrm{g}$ of water. Calculate $\Delta U$ per mole of $\mathrm{SO}_{2}$ formed, for the reaction
$$\mathrm{S}_{8}(\mathrm{s})+8 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 8 \mathrm{SO}_{2}(\mathrm{g})$$
PICTURE CANT COPY

Amany Waheeb

Numerade Educator

Problem 38

Suppose you burn $0.300 \mathrm{g}$ of $\mathrm{C}$ (graphite) in an excess of $\mathrm{O}_{2}(\mathrm{g})$ in a constant volume calorimeter to give $\mathrm{CO}_{2}(\mathrm{g})$
$$\text { C(graphite) }+\mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{CO}_{2}(\mathrm{g})$$
The temperature of the calorimeter, which contains
$775 \mathrm{g}$ of water, increases from $25.00^{\circ} \mathrm{C}$ to $27.38^{\circ} \mathrm{C}$
The heat capacity of the bomb is $893 \mathrm{J} / \mathrm{K}$. Calculate $\Delta U$ per mole of carbon.

Jean Gephart

Numerade Educator

Problem 39

Suppose you burn $1.500 \mathrm{g}$ of benzoic acid, $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CO}_{2} \mathrm{H}$ in a constant volume calorimeter and find that the temperature increases from $22.50^{\circ} \mathrm{C}$ to $31.69^{\circ} \mathrm{C} .$ The calorimeter contains 775 g of water, and the bomb has a heat capacity of $893 \mathrm{J} / \mathrm{K}$. Calculate $\Delta U$ per mole of benzoic acid.
FIGURE CANT COPY

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 40

A 0.692 -g sample of glucose, $\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}$, is burned in a constant volume calorimeter. The temperature rises from $21.70^{\circ} \mathrm{C}$ to $25.22^{\circ} \mathrm{C} .$ The calorimeter contains $575 \mathrm{g}$ of water, and the bomb has a heat capacity of $650 \mathrm{J} / \mathrm{K} .$ What is $\Delta U$ per mole of glucose?

Lottie Adams

Numerade Educator

Problem 41

An "ice calorimeter" can be used to determine the specific heat capacity of a metal. A piece of hot metal is dropped onto a weighed quantity of ice. The energy transferred from the metal to the ice can be determined from the amount of ice melted. Suppose you heat a 50.0 -g piece of silver to $99.8^{\circ} \mathrm{C}$ and then drop it onto ice. When the metal's temperature has dropped to $0.0^{\circ} \mathrm{C},$ it is found that $3.54 \mathrm{g}$ of ice has melted. What is the specific heat capacity of silver?

Alice .

Numerade Educator

Problem 42

A $9.36-\mathrm{g}$ piece of platinum is heated to $98.6^{\circ} \mathrm{C}$ in a boiling water bath and then dropped onto ice. (See Study Question 41.) When the metal's temperature has dropped to $0.0^{\circ} \mathrm{C},$ it is found that $0.37 \mathrm{g}$ of ice has melted. What is the specific heat capacity of platinum?

Adam Wade

Numerade Educator

Problem 43

The enthalpy changes for the following reactions can be measured:
$$\begin{array}{l}
\mathrm{CH}_{4}(\mathrm{g})+2 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{CO}_{2}(\mathrm{g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \\
\qquad \Delta_{\mathrm{r}} H^{\circ}=-802.4 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn} \\
\mathrm{CH}_{3} \mathrm{OH}(\mathrm{g})+3 / 2 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{CO}_{2}(\mathrm{g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \\
\quad \Delta_{r} H^{\circ}=-676 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}
\end{array}$$
(a) Use these values and Hess's law to determine the enthalpy change for the reaction
$$\mathrm{CH}_{4}(\mathrm{g})+1 / 2 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{CH}_{3} \mathrm{OH}(\mathrm{g})$$
(b) Draw an energy-level diagram that shows the relationship between the energy quantities involved in this problem.

Amany Waheeb

Numerade Educator

Problem 44

The enthalpy changes of the following reactions can be measured:
$$\begin{aligned}
\mathrm{C}_{2} \mathrm{H}_{4}(\mathrm{g})+3 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{CO}_{2}(\mathrm{g}) &+2 \mathrm{H}_{2} \mathrm{O}(\ell) \\
\Delta_{r} H^{\circ} &=-1411.1 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn} \\
\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(\ell)+3 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{CO}_{2}(\mathrm{g}) &+3 \mathrm{H}_{2} \mathrm{O}(\ell) \\
\Delta_{r} H^{\circ} &=-1367.5 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}
\end{aligned}$$
(a) Use these values and Hess's law to determine the enthalpy change for the reaction
$$\mathrm{C}_{2} \mathrm{H}_{4}(\mathrm{g})+\mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(\ell)$$
(b) Draw an energy-level diagram that shows the relationship between the energy quantities involved in this problem.

Maryam Shahid

Numerade Educator

Problem 45

Enthalpy changes for the following reactions can be determined experimentally:
$\mathrm{N}_{2}(\mathrm{g})+3 \mathrm{H}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{NH}_{3}(\mathrm{g})$
$$\begin{array}{r}
\Delta_{r} H^{\circ}=-91.8 \mathrm{kJ} / / \mathrm{mol}-\mathrm{rxn} \\
4 \mathrm{NH}_{3}(\mathrm{g})+5 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 4 \mathrm{NO}(\mathrm{g})+6 \mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \\
\Delta_{r} H^{\circ}=-906.2 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}
\end{array}
$$$\mathrm{H}_{2}(\mathrm{g})+1 / 2 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{H}_{2} \mathrm{O}(\mathrm{g})$
$$\Delta_{r} H^{\circ}=-241.8 \mathrm{kJ} / / \mathrm{mol}-\mathrm{rxn}$$
Use these values to determine the enthalpy change for the formation of $\mathrm{NO}(\mathrm{g})$ from the elements (an enthalpy change that cannot be measured directly because the reaction is reactant-favored).
$$1 / 2 \mathrm{N}_{2}(\mathrm{g})+1 / 2 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{NO}(\mathrm{g}) \quad \Delta_{\mathrm{r}} H^{\circ}=?$$

Maryam Shahid

Numerade Educator

Problem 46

You wish to know the enthalpy change for the formation of liquid PCl _ from the elements.
$$
\mathrm{P}_{4}(\mathrm{s})+6 \mathrm{Cl}_{2}(\mathrm{g}) \rightarrow 4 \mathrm{PCl}_{3}(\ell) \quad \Delta_{\mathrm{r}} H^{\circ}=?
$$
The enthalpy change for the formation of $\mathrm{PCl}_{5}$ from the elements can be determined experimentally, as can the enthalpy change for the reaction of $\mathrm{PCl}_{3}(\ell)$ with more chlorine to give $\mathrm{PCl}_{5}(\mathrm{s}):$ $\mathrm{P}_{4}(\mathrm{s})+10 \mathrm{Cl}_{2}(\mathrm{g}) \rightarrow 4 \mathrm{PCl}_{5}(\mathrm{s})$
$$\Delta_{\mathrm{r}} H^{\circ}=-1774.0 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}
$$$\mathrm{PCl}_{3}(\ell)+\mathrm{Cl}_{2}(\mathrm{g}) \rightarrow \mathrm{PCl}_{5}(\mathrm{s})$
$$\Delta_{r} H^{\circ}=-123.8 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}
$$Use these data to calculate the enthalpy change for the formation of 1.00 mol of $\mathrm{PCl}_{3}(\ell)$ from phosphorus and chlorine.

Maryam Shahid

Numerade Educator

Problem 47

Write a balanced chemical equation for the formation of $\mathrm{CH}_{3} \mathrm{OH}(\ell)$ from the elements in their standard states. Find the value for $\Delta_{f} H^{\circ}$ for $\mathrm{CH}_{3} \mathrm{OH}(\ell)$ in Appendix L.

Alice .

Numerade Educator

Problem 48

Write a balanced chemical equation for the formation of $\mathrm{CaCO}_{3}(\mathrm{s})$ from the elements in their standard states. Find the value for $\Delta_{f} H^{\circ}$ for $\mathrm{CaCO}_{3}(\mathrm{s})$ in Appendix $\mathrm{L}$

Bin Chen

Numerade Educator

Problem 49

(a) Write a balanced chemical equation for the formation of 1 mol of $\mathrm{Cr}_{2} \mathrm{O}_{3}(\mathrm{s})$ from $\mathrm{Cr}$ and $\mathrm{O}_{2}$ in their standard states. Find the value for $\Delta_{f} H^{\circ}$ for $\mathrm{Cr}_{2} \mathrm{O}_{3}(\mathrm{s})$ in Appendix L.
(b) $\overline{\mathbf{z}}$ What is the standard enthalpy change if $2.4 \mathrm{g}$ of chromium is oxidized to $\mathrm{Cr}_{2} \mathrm{O}_{3}(\mathrm{s}) ?$

Maryam Shahid

Numerade Educator

Problem 50

(a) Write a balanced chemical equation for the formation of 1 mol of $\mathrm{MgO}(\mathrm{s})$ from the elements in their standard states. Find the value for $\Delta_{j} H^{\circ}$ for $\mathrm{MgO}(\mathrm{s})$ in Appendix L.
(b) What is the standard enthalpy change for the reaction of 2.5 mol of Mg with oxygen?

Bin Chen

Numerade Educator

Problem 51

Use standard enthalpies of formation in Appendix L to calculate enthalpy changes for the following:
(a) $1.0 \mathrm{g}$ of white phosphorus burns, forming $\mathrm{P}_{4} \mathrm{O}_{10}(\mathrm{s})$
(b) 0.20 mol of $\mathrm{NO}(\mathrm{g})$ decomposes to $\mathrm{N}_{2}(\mathrm{g})$ and $\mathrm{O}_{2}(\mathrm{g})$
(c) $2.40 \mathrm{g}$ of $\mathrm{NaCl}(\mathrm{s})$ is formed from $\mathrm{Na}(\mathrm{s})$ and excess $\mathrm{Cl}_{2}(\mathrm{g})$
(d) $250 \mathrm{g}$ of iron is oxidized with oxygen to $\mathrm{Fe}_{2} \mathrm{O}_{3}(\mathrm{s})$

Maryam Shahid

Numerade Educator

Problem 52

Use standard enthalpies of formation in Appendix $L$ to calculate enthalpy changes for the following:
(a) 0.054 g of sulfur burns, forming $\mathrm{SO}_{2}(\mathrm{g})$
(b) 0.20 mol of $\mathrm{HgO}(\mathrm{s})$ decomposes to $\mathrm{Hg}(\ell)$ and $\mathrm{O}_{2}(\mathrm{g})$
(c) $2.40 \mathrm{g}$ of $\mathrm{NH}_{3}(\mathrm{g})$ is formed from $\mathrm{N}_{2}(\mathrm{g})$ and excess $\mathrm{H}_{2}(\mathrm{g})$
(d) $1.05 \times 10^{-2}$ mol of carbon is oxidized to $\mathrm{CO}_{2}(\mathrm{g})$

Maryam Shahid

Numerade Educator

Problem 53

The first step in the production of nitric acid from ammonia involves the oxidation of $\mathrm{NH}_{3}$
$$4 \mathrm{NH}_{3}(\mathrm{g})+5 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 4 \mathrm{NO}(\mathrm{g})+6 \mathrm{H}_{2} \mathrm{O}(\mathrm{g})$$
(a) Use standard enthalpies of formation to calculate the standard enthalpy change for this reaction.
(b) How much energy as heat is evolved or absorbed in the oxidation of $10.0 \mathrm{g}$ of $\mathrm{NH}_{3} ?$

Bin Chen

Numerade Educator

Problem 54

The Romans used calcium oxide, CaO, to produce a strong mortar to build stone structures. The CaO was mixed with water to give $\mathrm{Ca}(\mathrm{OH})_{2},$ which reacted slowly with $\mathrm{CO}_{2}$ in the air to give $\mathrm{CaCO}_{3}$
$$\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{s})+\mathrm{CO}_{2}(\mathrm{g}) \rightarrow \mathrm{CaCO}_{3}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\mathrm{g})$$
(a) Calculate the standard enthalpy change for this reaction.
(b) How much energy as heat is evolved or absorbed if $1.00 \mathrm{kg}$ of $\mathrm{Ca}(\mathrm{OH})_{2}$ reacts with a stoichiometric amount of $\mathrm{CO}_{2} ?$

Maryam Shahid

Numerade Educator

Problem 55

The standard enthalpy of formation of solid barium oxide, $\mathrm{BaO},$ is $-553.5 \mathrm{kJ} / \mathrm{mol},$ and the standard enthalpy of formation of barium peroxide, $\mathrm{BaO}_{2},$ is $-634.3 \mathrm{kJ} / \mathrm{mol}$
(a) Calculate the standard enthalpy change for the following reaction. Is the reaction exothermic or endothermic?
$$2 \mathrm{BaO}_{2}(\mathrm{s}) \rightarrow 2 \mathrm{BaO}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{g})$$
(b) Draw an energy-level diagram that shows the relationship between the enthalpy change of the decomposition of $\mathrm{BaO}_{2}$ to $\mathrm{BaO}$ and $\mathrm{O}_{2}$ and the enthalpies of formation of $\mathrm{BaO}(\mathrm{s})$ and $\mathrm{BaO}_{2}(\mathrm{s})$

Maryam Shahid

Numerade Educator

Problem 56

An important step in the production of sulfuric acid is the oxidation of $\mathrm{SO}_{2}$ to $\mathrm{SO}_{3}$
$$\mathrm{SO}_{2}(\mathrm{g})+1 / 2 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{SO}_{3}(\mathrm{g})$$
Formation of $\mathrm{SO}_{3}$ from the air pollutant $\mathrm{SO}_{2}$ is also a key step in the formation of acid rain.
(a) Use standard enthalpies of formation to calculate the enthalpy change for the reaction. Is the reaction exothermic or endothermic?
(b) Draw an energy-level diagram that shows the relationship between the enthalpy change for the oxidation of $\mathrm{SO}_{2}$ to $\mathrm{SO}_{3}$ and the enthalpies of formation of $\mathrm{SO}_{2}(\mathrm{g})$ and $\mathrm{SO}_{3}(\mathrm{g})$

Maryam Shahid

Numerade Educator

Problem 57

The enthalpy change for the oxidation of naphthalene, $\mathrm{C}_{10} \mathrm{H}_{8},$ is measured by calorimetry.$$\begin{aligned}
\mathrm{C}_{10} \mathrm{H}_{8}(\mathrm{s})+12 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 10 \mathrm{CO}_{2}(\mathrm{g})+4 \mathrm{H}_{2} \mathrm{O}(\ell) &+\\
\Delta_{r} H^{0}=&-5156.1 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}\end{aligned}$$
Use this value, along with the standard enthalpies of formation of $\mathrm{CO}_{2}(\mathrm{g})$ and $\mathrm{H}_{2} \mathrm{O}(\ell),$ to calculate the enthalpy of formation of naphthalene, in $\mathrm{kJ} / \mathrm{mol}$.

Maryam Shahid

Numerade Educator

Problem 58

The enthalpy change for the oxidation of styrene, $\mathrm{C}_{8} \mathrm{H}_{8},$ is measured by calorimetry. $\mathrm{C}_{8} \mathrm{H}_{8}(\ell)+10 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 8 \mathrm{CO}_{2}(\mathrm{g})+4 \mathrm{H}_{2} \mathrm{O}(\ell)$
$$\Delta_{r} H^{\circ}=-4395.0 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}$$
Use this value, along with the standard enthalpies of formation of $\mathrm{CO}_{2}(\mathrm{g})$ and $\mathrm{H}_{2} \mathrm{O}(\ell),$ to calculate the enthalpy of formation of styrene, in $\mathrm{k} \mathrm{J} / \mathrm{mol}$.

Maryam Shahid

Numerade Educator

Problem 59

The following terms are used extensively in thermodynamics. Define each and give an example.
(a) exothermic and endothermic
(b) system and surroundings
(c) specific heat capacity
(d) state function
(e) standard state
(f) enthalpy change, $\Delta H$
(g) standard enthalpy of formation

Banhishikha Sinha

Banhishikha Sinha

Numerade Educator

Problem 60

For each of the following, tell whether the process is exothermic or endothermic. (No calculations are required.)
(a) $\mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow \mathrm{H}_{2} \mathrm{O}(\mathrm{s})$
(b) $2 \mathrm{H}_{2}(\mathrm{g})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{H}_{2} \mathrm{O}(\mathrm{g})$
(c) $\mathrm{H}_{2} \mathrm{O}\left(\ell, 25^{\circ} \mathrm{C}\right) \rightarrow \mathrm{H}_{2} \mathrm{O}\left(\ell, 15^{\circ} \mathrm{C}\right)$
(d) $\mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow \mathrm{H}_{2} \mathrm{O}(\mathrm{g})$

Bin Chen

Numerade Educator

Problem 61

For each of the following, define a system and its surroundings, and give the direction of energy transfer between system and surroundings.
(a) Methane is burning in a gas furnace in your home.
(b) Water drops, sitting on your skin after a dip in a swimming pool, evaporate.
(c) Water, at $25^{\circ} \mathrm{C},$ is placed in the freezing compartment of a refrigerator, where it cools and eventually solidifies.
(d) Aluminum and $\mathrm{Fe}_{2} \mathrm{O}_{3}(\mathrm{s})$ are mixed in a flask sitting on a laboratory bench. A reaction occurs, and a large quantity of energy is evolved as heat.

Bin Chen

Numerade Educator

Problem 62

What does the term "standard state" mean? What are the standard states of the following substances at $298 \mathrm{K}: \mathrm{H}_{2} \mathrm{O}, \mathrm{NaCl}, \mathrm{Hg}, \mathrm{CH}_{4} ?$

Bin Chen

Numerade Educator

Problem 63

Use Appendix $L$ to find the standard enthalpies of formation of oxygen atoms, oxygen molecules $\left(\mathbf{O}_{2}\right)$ and ozone $\left(\mathrm{O}_{3}\right) .$ What is the standard state of oxygen? Is the formation of oxygen atoms from $\mathrm{O}_{2}$ exothermic? What is the enthalpy change for the formation of
$1 \mathrm{mol}$ of $\mathrm{O}_{3}$ from $\mathrm{O}_{2} ?$

Alice .

Numerade Educator

Problem 64

See the ChemistryNow website, Screen $5.9,$ Heat Transfer Between Substances. Use the Simulation section of this screen to do the following experiment:
Add $10.0 \mathrm{g}$ of $\mathrm{Al}$ at $80^{\circ} \mathrm{C}$ to $10.0 \mathrm{g}$ of water at $20^{\circ} \mathrm{C}$ What is the final temperature when equilibrium is achieved? Use this value to estimate the specific heat capacity of aluminum.

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 65

See the ChemistryNow website, Screen $5.15,$ Hess's Law. Use the Simulation section of this screen to find the value of $\Delta_{\mathrm{r}} H^{\circ}$ for
$\operatorname{SnBr}_{2}(\mathrm{s})+\mathrm{TiCl}_{4}(\ell) \rightarrow \mathrm{SnCl}_{4}(\ell)+\operatorname{TiBr}_{2}(\mathrm{s})$

Banhishikha Sinha

Banhishikha Sinha

Numerade Educator

Problem 66

Which gives up more energy on cooling from $50^{\circ} \mathrm{C}$ to
$10^{\circ} \mathrm{C}, 50.0 \mathrm{g}$ of water or $100 . \mathrm{g}$ of ethanol (specific heat capacity of ethanol $=2.46 \mathrm{J} / \mathrm{g} \cdot \mathrm{K}) ?$

Alice .

Numerade Educator

Problem 67

You determine that $187 \mathrm{J}$ of heat is required to raise the temperature of $93.45 \mathrm{g}$ of silver from $18.5^{\circ} \mathrm{C}$ to $27.0^{\circ} \mathrm{C} .$ What is the specific heat capacity of silver?

Alice .

Numerade Educator

Problem 68

Calculate the quantity of energy required to convert $60.1 \mathrm{g}$ of $\mathrm{H}_{2} \mathrm{O}(\mathrm{s})$ at $0.0^{\circ} \mathrm{C}$ to $\mathrm{H}_{2} \mathrm{O}(\mathrm{g})$ at $100.0^{\circ} \mathrm{C}$
The heat of fusion of ice at $0^{\circ} \mathrm{C}$ is $333 \mathrm{J} / \mathrm{g} ;$ the heat of vaporization of liquid water at $100^{\circ} \mathrm{C}$ is $2260 \mathrm{J} / \mathrm{g} .$

Arun Bana

Numerade Educator

Problem 69

You add $100.0 \mathrm{g}$ of water at $60.0^{\circ} \mathrm{C}$ to $100.0 \mathrm{g}$ of ice at $0.00^{\circ} \mathrm{C} .$ Some of the ice melts and cools the water to $0.00^{\circ} \mathrm{C} .$ When the ice and water mixture has come to a uniform temperature of $0^{\circ} \mathrm{C},$ how much ice has melted?

Alice .

Numerade Educator

Problem 70

A Three $45-\mathrm{g}$ ice cubes at $0^{\circ} \mathrm{C}$ are dropped into $5.00 \times 10^{2} \mathrm{mL}$ of tea to make iced tea. The tea was initially at $20.0^{\circ} \mathrm{C} ;$ when thermal equilibrium was reached, the final temperature was $0^{\circ} \mathrm{C} .$ How much of the ice melted, and how much remained floating in the beverage? Assume the specific heat capacity of tea is the same as that of pure water.

Bin Chen

Numerade Educator

Problem 71

A Suppose that only two 45 -g ice cubes had been added to your glass containing $5.00 \times 10^{2} \mathrm{mL}$ of tea (see Study Question 70 ). When thermal equilibrium is reached, all of the ice will have melted, and the temperature of the mixture will be somewhere between $20.0^{\circ} \mathrm{C}$ and $0^{\circ} \mathrm{C} .$ Calculate the final temperature of the beverage. (Note: The 90 g of water formed when the ice melts must be warmed from $0^{\circ} \mathrm{C}$ to the final temperature.)

David Collins

Numerade Educator

Problem 72

You take a diet cola from the refrigerator and pour 240 mL of it into a glass. The temperature of the beverage is $10.5^{\circ} \mathrm{C} .$ You then add one ice cube $(45 \mathrm{g}) .$ Which of the following describes the system when thermal equilibrium is reached?
(a) The temperature is $0^{\circ} \mathrm{C},$ and some ice remains.
(b) The temperature is $0^{\circ} \mathrm{C},$ and no ice remains.
(c) The temperature is higher than $0^{\circ} \mathrm{C},$ and no ice remains.
Determine the final temperature and the amount of ice remaining, if any.

Banhishikha Sinha

Banhishikha Sinha

Numerade Educator

Problem 73

A The standard molar enthalpy of formation of diborane, $\mathrm{B}_{2} \mathrm{H}_{6}(\mathrm{g}),$ cannot be determined directly because the compound cannot be prepared by the reaction of boron and hydrogen. It can be calculated from other enthalpy changes, however. The following enthalpy changes can be measured.
$$\begin{array}{l}
4 \mathrm{B}(\mathrm{s})+3 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{B}_{2} \mathrm{O}_{3}(\mathrm{s}) \\
\quad \mathrm{A}_{r} H^{\circ}=-2543.8 \mathrm{kJ} / \mathrm{mol}-\mathrm{r} \times \mathrm{n} \\
\mathrm{H}_{2}(\mathrm{g})+1 / 2 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \Delta_{r} H^{\circ}=-241.8 \mathrm{kJ} / \mathrm{mol}-\mathrm{r} \mathrm{xn} \\
\mathrm{B}_{2} \mathrm{H}_{6}(\mathrm{g})+3 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{B}_{2} \mathrm{O}_{3}(\mathrm{s})+3 \mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \\
\quad \Delta_{r} H^{\circ}=-2032.9 \mathrm{kJ} / \mathrm{mol}-\mathrm{r} \times \mathrm{n}
\end{array}$$
(a) Show how these equations can be added together to give the equation for the formation of $\mathrm{B}_{2} \mathrm{H}_{6}(\mathrm{g})$ from $\mathrm{B}(\mathrm{s})$ and $\mathrm{H}_{2}(\mathrm{g})$ in their standard states. Assign enthalpy changes to each reaction.
(b) Calculate $\Delta_{f} H^{\circ}$ for $\mathrm{B}_{2} \mathrm{H}_{6}(\mathrm{g})$
(c) Draw an energy-level diagram that shows how the various enthalpies in this problem are related.
(d) Is the formation of $\mathrm{B}_{2} \mathrm{H}_{6}(\mathrm{g})$ from its elements product-favored or reactant-favored?

Tom Comey

Numerade Educator

Problem 74

Chloromethane, $\mathrm{CH}_{3} \mathrm{Cl}$, a compound found ubiquitously in the environment, is formed in the reaction of chlorine atoms with methane.
$$\mathrm{CH}_{4}(\mathrm{g})+2 \mathrm{Cl}(\mathrm{g}) \rightarrow \mathrm{CH}_{3} \mathrm{Cl}(\mathrm{g})+\mathrm{HCl}(\mathrm{g})$$
(a) Calculate the enthalpy change for the reaction of $\mathrm{CH}_{4}(\mathrm{g})$ and $\mathrm{Cl}$ atoms to give $\mathrm{CH}_{3} \mathrm{Cl}(\mathrm{g})$ and
HCl (g). Is the reaction product-favored or reactantfavored?
(b) Draw an energy-level diagram that shows how the various enthalpies in this problem are related.

Bin Chen

Numerade Educator

Problem 75

When heated to a high temperature, coke (mainly carbon, obtained by heating coal in the absence of air) and steam produce a mixture called water gas, which can be used as a fuel or as a chemical feedstock for other reactions. The equation for the production of water gas is
$$\mathrm{C}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \rightarrow \mathrm{CO}(\mathrm{g})+\mathrm{H}_{2}(\mathrm{g})$$
(a) Use standard enthalpies of formation to determine the enthalpy change for this reaction.
(b) Is the reaction product-favored or reactant-favored?
(c) What is the enthalpy change if 1.0 metric ton $(1000.0 \mathrm{kg})$ of carbon is converted to water gas?

Bin Chen

Numerade Educator

Problem 76

Camping stoves are fueled by propane $\left(\mathrm{C}_{3} \mathrm{H}_{8}\right),$ butane $\left[\mathrm{C}_{4} \mathrm{H}_{10}(\mathrm{g}), \Delta_{/} H^{\circ}=-127.1 \mathrm{kJ} / / \mathrm{mol}\right],$ gasoline, or etha-
nol $\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right) .$ Calculate the enthalpy of combustion per gram of each of these fuels. [Assume that gasoline is represented by isooctane, $\mathbf{C}_{8} \mathbf{H}_{18}(\ell),$ with $\Delta_{/} H^{\circ}=$
$-259.2 \mathrm{kJ} / \mathrm{mol.}]$ Do you notice any great differences among these fuels? Are these differences related to their composition?
PICTURE CANT COPY

Maryam Shahid

Numerade Educator

Problem 77

Methanol, $\mathrm{CH}_{3} \mathrm{OH},$ a compound that can be made relatively inexpensively from coal, is a promising substitute for gasoline. The alcohol has a smaller energy content than gasoline, but, with its higher octane rating, it burns more efficiently than gasoline in combustion engines. (It has the added advantage of contributing to a lesser degree to some air pollutants.) Compare the enthalpy of combustion per gram of $\mathrm{CH}_{3} \mathrm{OH}$ and $\mathrm{C}_{6} \mathrm{H}_{18}$ (isooctane), the latter being representative of the compounds in gasoline. $\left(\Delta_{j} H^{\circ}=-259.2 \mathrm{kJ} / / \mathrm{mol} \text { for isooctane. }\right)$

Bin Chen

Numerade Educator

Problem 78

Hydrazine and 1,1 -dimethylhydrazine both react spontaneously with $\mathrm{O}_{2}$ and can be used as rocket fuels.
$$\mathrm{N}_{2} \mathrm{H}_{4}(\ell)+\mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{N}_{2}(\mathrm{g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{g})$$
hydrazine
PICTURE CANT COPY
$\mathrm{N}_{2} \mathrm{H}_{2}\left(\mathrm{CH}_{3}\right)_{2}(\ell)+4 \mathrm{O}_{2}(\mathrm{g}) \rightarrow$
$$\text { 1,1-dimethylhydrazine } \quad 2 \mathrm{CO}_{2}(\mathrm{g})+4 \mathrm{H}_{2} \mathrm{O}(\mathrm{g})+\mathrm{N}_{2}(\mathrm{g})$$
The molar enthalpy of formation of $\mathrm{N}_{2} \mathrm{H}_{4}(\ell)$ is $+50.6 \mathrm{kJ} / \mathrm{mol},$ and that of $\mathrm{N}_{2} \mathrm{H}_{2}\left(\mathrm{CH}_{3}\right)_{2}(\ell)$ is
$+48.9 \mathrm{kJ} / \mathrm{mol} .$ Use these values, with other $\Delta_{f} H^{\circ}$ values, to decide whether the reaction of hydrazine or 1,1 -dimethylhydrazine with oxygen provides more energy per gram.

Bin Chen

Numerade Educator

Problem 79

(a) Calculate the enthalpy change, $\Delta_{r} H^{\circ}$, for the formation of 1.00 mol of strontium carbonate (the material that gives the red color in fireworks) from its elements.
$\mathrm{Sr}(\mathrm{s})+\mathrm{C}(\text { graphite })+3 / 2 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{SrCO}_{3}(\mathrm{s})$
The experimental information available is
$\mathrm{Sr}(\mathrm{s})+1 / 2 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{SrO}(\mathrm{s}) \quad \Delta_{f} H^{\circ}=-592 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}$
$\mathrm{SrO}(\mathrm{s})+\mathrm{CO}_{2}(\mathrm{g}) \rightarrow \mathrm{SrCO}_{3}(\mathrm{s}) \quad \Delta_{r} H^{\circ}=-234 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}$
C(graphite) $+\mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{CO}_{2}(\mathrm{g}) \quad \Delta_{f} H^{\circ}=-394 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}$
(b) Draw an energy-level diagram relating the energy quantities in this problem.

Maryam Shahid

Numerade Educator

Problem 80

You drink 350 mL of diet soda that is at a temperature of $5^{\circ} \mathrm{C}$
(a) How much energy will your body expend to raise the temperature of this liquid to body temperature $\left(37^{\circ} \mathrm{C}\right) ?$ Assume that the density and specific heat capacity of diet soda are the same as for water.
(b) Compare the value in part (a) with the caloric content of the beverage. (The label says that it has a caloric content of 1 Calorie.) What is the net energy change in your body resulting from drinking this beverage?
(c) Carry out a comparison similar to that in part (b) for a nondiet beverage whose label indicates a caloric content of 240 Calories.

Banhishikha Sinha

Banhishikha Sinha

Numerade Educator

Problem 81

A Chloroform, $\mathrm{CHCl}_{3}$, is formed from methane and chlorine in the following reaction.
$$\mathrm{CH}_{4}(\mathrm{g})+3 \mathrm{Cl}_{2}(\mathrm{g}) \rightarrow 3 \mathrm{HCl}(\mathrm{g})+\mathrm{CHCl}_{3}(\mathrm{g})$$
Calculate $\Delta_{\mathrm{r}} H^{\circ},$ the enthalpy change for this reaction, using the enthalpies of formation of $\mathrm{CO}_{2}(\mathrm{g}), \mathrm{H}_{2} \mathrm{O}(\ell)$
and $\mathrm{CHCl}_{3}(\mathrm{g})\left(\Delta_{f} H^{\circ}=-103.1 \mathrm{kJ} / / \mathrm{mol}\right),$ and the en-
thalpy changes for the following reactions:
$\mathrm{CH}_{4}(\mathrm{g})+2 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{CO}_{2}(\mathrm{g})$
$$\Delta_{\mathrm{r}} H^{\circ}=-890.4 \mathrm{kJ} / / \mathrm{mol}-\mathrm{rxn}$$$2 \mathrm{HCl}(\mathrm{g}) \rightarrow \mathrm{H}_{2}(\mathrm{g})+\mathrm{Cl}_{2}(\mathrm{g})$
$$\Delta_{r} H^{\circ}=+184.6 \mathrm{kJ} / / \mathrm{mol}-\mathrm{rxn}$$

Pam Owens

Numerade Educator

Problem 82

Water gas, a mixture of carbon monoxide and hydrogen, is produced by treating carbon (in the form of coke or coal) with steam at high temperatures. (See Question $75 .)$
$$\mathrm{C}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \rightarrow \mathrm{CO}(\mathrm{g})+\mathrm{H}_{2}(\mathrm{g})$$
Not all of the carbon available is converted to water gas since some is burned to provide the heat for the endothermic reaction of carbon and water. What mass of carbon must be burned (to $\mathrm{CO}_{2}$ gas) to provide the energy to convert $1.00 \mathrm{kg}$ of carbon to water gas?

Bin Chen

Numerade Educator

Problem 83

A piece of lead with a mass of $27.3 \mathrm{g}$ was heated to $98.90^{\circ} \mathrm{C}$ and then dropped into $15.0 \mathrm{g}$ of water at $22.50^{\circ} \mathrm{C} .$ The final temperature was $26.32^{\circ} \mathrm{C} .$ Calculate the specific heat capacity of lead from these data.

Banhishikha Sinha

Banhishikha Sinha

Numerade Educator

Problem 84

A $192-\mathrm{g}$ piece of copper is heated to $100.0^{\circ} \mathrm{C}$ in a boiling water bath and then dropped into a beaker containing $751 \mathrm{g}$ of water (density $=1.00 \mathrm{g} / \mathrm{cm}^{3}$ ) at $4.0^{\circ} \mathrm{C} .$ What is the final temperature of the copper and water after thermal equilibrium is reached? (The specific heat capacity of copper is $0.385 \mathrm{J} / \mathrm{g} \cdot \mathrm{K} .$ )

Banhishikha Sinha

Banhishikha Sinha

Numerade Educator

Problem 85

Insoluble AgCl(s) precipitates when solutions of $\mathrm{AgNO}_{3}(\mathrm{aq})$ and $\mathrm{NaCl}(\mathrm{aq})$ are mixed.
$$\mathrm{AgNO}_{3}(\mathrm{aq})+\mathrm{NaCl}(\mathrm{aq}) \rightarrow \mathrm{AgCl}(\mathrm{s})+\mathrm{NaNO}_{3}(\mathrm{aq})$$
To measure the energy evolved in this reaction, $250 . \mathrm{mL}$ of $0.16 \mathrm{M} \mathrm{AgNO}_{3}(\mathrm{aq})$ and $125 \mathrm{mL}$ of $0.32 \mathrm{M} \mathrm{NaCl}(\mathrm{aq})$
are mixed in a coffee-cup calorimeter. The temperature of the mixture rises from $21.15^{\circ} \mathrm{C}$ to $22.90^{\circ} \mathrm{C} .$ Calculate the enthalpy change for the precipitation of $\mathrm{AgCl}(\mathrm{s}),$ in kJ/mol. (Assume the density of the solution is $1.0 \mathrm{g} / \mathrm{mL}$ and its specific heat capacity is $4.2 \mathrm{J} / \mathrm{g} \cdot \mathrm{K} .$ )

Bin Chen

Numerade Educator

Problem 86

Insoluble $\mathrm{PbBr}_{2}(\mathrm{s})$ precipitates when solutions of $\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})$ and $\mathrm{NaBr}(\mathrm{aq})$ are mixed.
$$\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})+2 \mathrm{NaBr}(\mathrm{aq}) \rightarrow \mathrm{PbBr}_{2}(\mathrm{s})+2 \mathrm{NaNO}_{3}(\mathrm{aq})$$
To measure the enthalpy change, $200 .$ mL of $0.75 \mathrm{M}$ $\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})$ and $200 .$ mL of $1.5 \mathrm{M} \mathrm{NaBr}(\mathrm{aq})$ are
mixed in a coffee-cup calorimeter. The temperature of the mixture rises by $2.44^{\circ} \mathrm{C} .$ Calculate the enthalpy change for the precipitation of $\mathrm{PbBr}_{2}(\mathrm{s}),$ in $\mathrm{kJ} / \mathrm{mol}$. (Assume the density of the solution is $1.0 \mathrm{g} / \mathrm{mL}$ and its specific heat capacity is $4.2 \mathrm{J} / \mathrm{g} \cdot \mathrm{K}$.

Pam Owens

Numerade Educator

Problem 87

The value of $\Delta U$ in the decomposition of $7.647 \mathrm{g}$ of ammonium nitrate can be measured in a bomb calorimeter. The reaction that occurs is
$$\mathrm{NH}_{4} \mathrm{NO}_{3}(\mathrm{s}) \rightarrow \mathrm{N}_{2} \mathrm{O}(\mathrm{g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{g})$$
The temperature of the calorimeter, which contains $415 \mathrm{g}$ of water, increases from $18.90^{\circ} \mathrm{C}$ to $20.72^{\circ} \mathrm{C}$
The heat capacity of the bomb is $155 \mathrm{J} / \mathrm{K}$. What is the value of $\Delta U$ for this reaction, in $\mathrm{kJ} / \mathrm{mol}$ ?

Bin Chen

Numerade Educator

Problem 88

A bomb calorimetric experiment was run to determine the heat of combustion of ethanol (a common fuel additive). The reaction is
$$\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(\ell)+3 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{CO}_{2}(\mathrm{g})+3 \mathrm{H}_{2} \mathrm{O}(\ell)$$
The bomb had a heat capacity of $550 \mathrm{J} / \mathrm{K},$ and the calorimeter contained $650 \mathrm{g}$ of water. Burning $4.20 \mathrm{g}$ of ethanol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(\ell)$ resulted in a rise in temperature from $18.5^{\circ} \mathrm{C}$ to $22.3^{\circ} \mathrm{C} .$ Calculate the enthalpy of combustion of ethanol, in $\mathrm{kJ} / \mathrm{mol}$

Bin Chen

Numerade Educator

Problem 89

The meals-ready-to-eat (MREs) in the military can be heated on a flameless heater. You can purchase a similar product called "Heater Meals." Just pour water into the heater unit, wait a few minutes, and you have a hot meal. The source of energy in the heater is
$$\mathrm{Mg}(\mathrm{s})+2 \mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow \mathrm{Mg}(\mathrm{OH})_{2}(\mathrm{s})+\mathrm{H}_{2}(\mathrm{g})$$ Calculate the enthalpy change under standard conditions, in joules, for this reaction. What quantity of magnesium is needed to supply the energy required to warm 25 mL of water $(d=1.00 \mathrm{g} / \mathrm{mL})$ from $25^{\circ} \mathrm{C}$ to $85^{\circ} \mathrm{C} ?$ (See W. Jensen: Journal of Chemical Education, Vol. $77, \text { pp. } 713-717,2000 .)$
PICTURE CANT COPY

Lottie Adams

Numerade Educator

Problem 90

On a cold day, you can warm your hands with a "heat pad," a device that uses the oxidation of iron to produce energy as heat.
$$4 \mathrm{Fe}(\mathrm{s})+3 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{Fe}_{2} \mathrm{O}_{3}(\mathrm{s})$$ What mass of iron is needed to supply the energy required to warm 15 mL of water $(d=1.00 \mathrm{g} / \mathrm{mL})$ from $23^{\circ} \mathrm{C}$ to $37^{\circ} \mathrm{C} ?$
PICTURE CANT COPY

Arun Bana

Numerade Educator

Problem 91

Without doing calculations, decide whether each of the following is product-favored or reactant-favored.
(a) the combustion of natural gas
(b) the decomposition of glucose, $\mathbf{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6},$ to carbon and water

Alice .

Numerade Educator

Problem 92

Which of the following are state functions?
(a) the volume of a balloon
(b) the time it takes to drive from your home to your college or university
(c) the temperature of the water in a coffee cup
(d) the potential energy of a ball held in your hand

Banhishikha Sinha

Banhishikha Sinha

Numerade Educator

Problem 93

A You want to determine the value for the enthalpy of formation of $\operatorname{CaSO}_{4}(\mathrm{s})$
$$\mathrm{Ca}(\mathrm{s})+\mathrm{S}(\mathrm{s})+2 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{CaSO}_{4}(\mathrm{s})$$
This reaction cannot be done directly. You know, however, that both calcium and sulfur react with oxygen to produce oxides in reactions that can be studied calorimetrically. You also know that the basic oxide $\mathrm{CaO}$ reacts with the acidic oxide $\mathrm{SO}_{3}(\mathrm{g})$ to produce $\mathrm{CaSO}_{4}(\mathrm{s})$ with $\Delta_{r} H^{\circ}=-402.7 \mathrm{kJ} .$ Outline a method for determining $\Delta_{f} H^{\circ}$ for $\mathrm{CaSO}_{4}(\mathrm{s}),$ and identify the information that must be collected by experiment. Using information in Appendix $\mathrm{L},$ confirm that $\Delta_{f} H^{\circ}$ for $\mathrm{CaSO}_{4}(\mathrm{s})=-1433.5 \mathrm{kJ} / \mathrm{mol}$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 94

Prepare a graph of specific heat capacities for metals versus their atomic weights. Combine the data in Figure 5.7 and the values in the following table. What is the relationship between specific heat capacity and atomic weight? Use this relationship to predict the specific heat capacity of platinum. The specific heat capacity for platinum is given in the literature as $0.133 \mathrm{J} / \mathrm{g} \cdot \mathrm{K}$ How good is the agreement between the predicted and actual values?
Metal Specific Heat Capacity $\mathrm{G} / \mathrm{g} \cdot \mathbf{K}$ ) $\begin{array}{lc}\text { Stal } & \text { Specific Heat Capacity } \overline{\mathrm{J}} \text { s } \\ \text { Chromium } & 0.450 \\ \text { Lead } & 0.127 \\ \text { Silver } & 0.236 \\ \text { Tin } & 0.227 \\ \text { Titanium } & 0.522\end{array}$

Pam Owens

Numerade Educator

Problem 95

Observe the molar heat capacity values for the metals in Figure $5.7 .$ What observation can you make about these values- specifically, are they widely different or very similar? Using this information, estimate the specific heat capacity for silver. Compare this estimate with the correct value for silver, $0.236 \mathrm{J} / \mathrm{g} \cdot \mathrm{K}$

Bin Chen

Numerade Educator

Problem 96

A Suppose you are attending summer school and are living in a very old dormitory. The day is oppressively hot. There is no air-conditioner, and you can't open the windows of your room because they are stuck shut from layers of paint. There is a refrigerator in the room, however. In a stroke of genius, you open the door of the refrigerator, and cool air cascades out. The relief does not last long, though. Soon the refrigerator motor and condenser begin to run, and not long thereafter the room is hotter than it was before. Why did the room warm up?

Pam Owens

Numerade Educator

Problem 97

You want to heat the air in your house with natural gas $\left(\mathrm{CH}_{4}\right) .$ Assume your house has $275 \mathrm{m}^{2}$ (about 2800 $\left.\mathrm{ft}^{2}\right)$ of floor area and that the ceilings are $2.50 \mathrm{m}$ from the floors. The air in the house has a molar heat capacity of $29.1 \mathrm{J} / \mathrm{mol} \cdot \mathrm{K}$. (The number of moles of air in the house can be found by assuming that the average molar mass of air is $28.9 \mathrm{g} / \mathrm{mol}$ and that the density of air at these temperatures is $1.22 \mathrm{g} / \mathrm{L} .$ ) What mass of methane do you have to burn to heat the air from 15.0
$^{\circ} \mathrm{C}$ to $22.0^{\circ} \mathrm{C} ?$

Bin Chen

Numerade Educator

Problem 98

Water can be decomposed to its elements, $\mathrm{H}_{2}$ and $\mathrm{O}_{2}$ using electrical energy or in a series of chemical reactions. The following sequence of reactions is one possibility:
$$\begin{array}{c}
\operatorname{CaBr}_{2}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \rightarrow \mathrm{CaO}(\mathrm{s})+2 \mathrm{HBr}(\mathrm{g}) \\
\mathrm{Hg}(\ell)+2 \mathrm{HBr}(\mathrm{g}) \rightarrow \operatorname{HgBr}_{2}(\mathrm{s})+\mathrm{H}_{2}(\mathrm{g}) \\
\mathrm{HgBr}_{2}(\mathrm{s})+\mathrm{CaO}(\mathrm{s}) \rightarrow \mathrm{HgO}(\mathrm{s})+\operatorname{CaBr}_{2}(\mathrm{s}) \\
\mathrm{HgO}(\mathrm{s}) \rightarrow \mathrm{Hg}(\ell)+1 / 2 \mathrm{O}_{2}(\mathrm{g})
\end{array}$$
(a) Show that the net result of this series of reactions is the decomposition of water to its elements.
(b) If you use $1000 .$ kg of water, what mass of $\mathrm{H}_{2}$ can be produced?
(c) Calculate the value of $\Delta_{r} H^{\circ}$ for each step in the series. Are the reactions predicted to be productfavored or reactant-favored?
$$\begin{aligned}
\Delta_{j} H^{\circ} &\left[\mathrm{CaBr}_{2}(\mathrm{s})\right]=-683.2 \mathrm{kJ} / / \mathrm{mol} \\
\Delta_{f} H^{\circ}\left[\mathrm{HgBr}_{2}(\mathrm{s})\right] &=-169.5 \mathrm{kJ} / \mathrm{mol}
\end{aligned}$$
(e) Comment on the commercial feasibility of using this series of reactions to produce $\mathrm{H}_{2}(\mathrm{g})$ from water.

Nicole Smina

Numerade Educator

Problem 99

Suppose that an inch of rain falls over a square mile of ground. (Density of water is $1.0 \mathrm{g} / \mathrm{cm}^{3} .$ ) The enthalpy of vaporization of water at $25^{\circ} \mathrm{C}$ is $44.0 \mathrm{kJ} / \mathrm{mol} .$ How much energy as heat is transferred to the surroundings from the condensation of water vapor in forming this quantity of liquid water? (The huge number tells you how much energy is "stored" in water vapor and why we think of storms as such great forces of energy in nature. It is interesting to compare this result with the energy given off, $4.2 \times 10^{6} \mathrm{kJ},$ when a ton of dynamite explodes.)

Victor Salazar

Numerade Educator

Problem 100

A Peanuts and peanut oil are organic materials and burn in air. How many burning peanuts does it take to provide the energy to boil a cup of water (250 mL of water)? To solve this problem, we assume each peanut, with an average mass of $0.73 \mathrm{g},$ is $49 \%$ peanut oil and $21 \%$ starch; the remainder is noncombustible. We further assume peanut oil is palmitic acid, $\mathrm{C}_{16} \mathrm{H}_{32} \mathrm{O}_{2},$ with an enthalpy of formation of $-848.4 \mathrm{kJ} / \mathrm{mol} .$ Starch is a long chain of $\mathrm{C}_{6} \mathrm{H}_{10} \mathrm{O}_{5}$
units, each unit having an enthalpy of formation of
$-960 \mathrm{kJ} .$ (See ChemistryNow Screens 5.1 and 5.19:
Chemical Puzzler.)
PICTURE CANT COPY

Victor Salazar

Numerade Educator

Problem 101

A Isomers are molecules with the same elemental composition but a different atomic arrangement. Three isomers with the formula $\mathrm{C}_{4} \mathrm{H}_{8}$ are shown in the models below. The enthalpy of combustion $\left(\Delta_{c} H^{\circ}\right)$ of each isomer, determined using a calorimeter, is:
$$\begin{array}{ll}\text { Compound } & \Delta_{\operatorname{com}} H^{\circ}(\mathrm{kJ} / \mathrm{mol}-\mathrm{r} \times \mathrm{n}) \\\hline \text {cis-} 2 \text { butene } & -2687.5 \\\text {trans-} 2 \text { -butene} & -2684.2 \\1 \text { -butene } & -2696.7 \\\hline\end{array}$$
(a) Draw an energy level diagram relating the energy content of the three isomers to the energy content of the combustion products, $\mathrm{CO}_{2}(\mathrm{g})$ and $\mathrm{H}_{2} \mathrm{O}(\mathrm{g})$
(b) Use the $\Delta_{c} H^{\circ}$ data in part (a), along with the enthalpies of formation of $\mathrm{CO}_{2}(\mathrm{g})$ and $\mathrm{H}_{2} \mathrm{O}(\mathrm{g})$ from Appendix $L$, to calculate the enthalpy of formation for each of the isomers.
(c) Draw an energy level diagram that relates the enthalpies of formation of the three isomers to the energy of the elements in their standard states.
(d) What is the enthalpy change for the conversion of cis-2-butene to trans-2-butene?
FIGURE CANT COPY

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 102

Several standard enthalpies of formation (from Appendix $L$ ) are given below. Use these data to calculate:
(a) The standard enthalpy of vaporization of bromine.
(b) The energy required for the reaction $\operatorname{Br}_{2}(\mathrm{g}) \rightarrow$ $2 \mathrm{Br}(\mathrm{g}) .$ (This is the $\mathrm{Br}-$ Br bond energy.)
$$\begin{array}{lc}\text { Species } & \Delta_{f} H^{\circ}(\mathrm{kJ} / \mathrm{mol}) \\
\hline \mathrm{Br}(\mathrm{g}) & 111.9 \\\mathrm{Br}_{2}(\ell) & 0 \\\mathrm{Br}_{2}(\mathrm{g}) & 30.9 \\\hline\end{array}$$

David Collins

Numerade Educator

Problem 103

When $0.850 \mathrm{g}$ of $\mathrm{Mg}$ is burned in oxygen in a constant volume calorimeter, $25.4 \mathrm{kJ}$ of energy as heat is evolved. The calorimeter is in an insulated container with $750 .$ g of water at an initial temperature of $18.6^{\circ} \mathrm{C}$ The heat capacity of the calorimeter is $820 . \mathrm{J} / \mathrm{K}$
(a) Calculate $\Delta \mathrm{U}$ for the oxidation of $\mathrm{Mg}$ $(\text { in } \mathrm{k} \mathrm{J} / \mathrm{mol} \mathrm{Mg})$
(b) What will be the final temperature of the water and the bomb calorimeter in this experiment?

Victor Salazar

Numerade Educator

Problem 104

A piece of gold $(10.0 \mathrm{g}, C=0.129 \mathrm{J} / \mathrm{g} \cdot \mathrm{K})$ is heated
to $100.0^{\circ} \mathrm{C} .$ A piece of copper (also $10.0 \mathrm{g}, C=0.385$ $\mathrm{J} / \mathrm{g} \cdot \mathrm{K})$ is chilled in an ice bath to $0^{\circ} \mathrm{C} .$ Both pieces of metal are placed in a beaker containing $150 .$ g $\mathrm{H}_{2} \mathrm{O}$ at $20^{\circ} \mathrm{C} .$ Will the temperature of the water be greater than or less than $20^{\circ} \mathrm{C}$ when thermal equilibrium is reached? Calculate the final temperature.

Arun Bana

Numerade Educator

Problem 105

Methane, $\mathrm{CH}_{4},$ can be converted to methanol which, like ethanol, can be used as a fuel. The energy level diagram shown here presents relationships between energies of the fuels and their oxidation products. Use the information in the diagram to answer the following questions. (The energy terms are per mol-rxn.)
(a) Which fuel, methanol or methane, yields the most energy per mole when burned?
(b) Which fuel yields the most energy per gram when burned?
(c) What is the enthalpy change for the conversion of methane to methanol?
(d) Each arrow on the diagram represents a chemical reaction. Write the equation for the reaction that converts methane to methanol.
GRAPH CANT COPY

Victor Salazar

Numerade Educator

Problem 106

Calculate $\Delta_{r} H^{\circ}$ for the reaction
$2 \mathrm{C}(\mathrm{s})+3 \mathrm{H}_{2}(\mathrm{g})+1 / 2 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(\ell)$
given the information below.
$$
\begin{array}{l}
\mathrm{C}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{CO}_{2}(\mathrm{g}) \quad \Delta_{\mathrm{r}} H^{\circ}=-393.5 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn} \\
2 \mathrm{H}_{2}(\mathrm{g})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{H}_{2} \mathrm{O}(\ell) \\
\quad \Delta_{r} H^{\ominus}=-571.6 \mathrm{kJ} / \mathrm{mol}-\mathrm{r} \mathrm{xn} \\
\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(\ell)+3 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{CO}_{2}(\mathrm{g})+3 \mathrm{H}_{2} \mathrm{O}(\ell) \\
\quad \Delta_{\mathrm{r}} \mathrm{H}^{\circ}=-1367.5 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}
\end{array}$$

Diwakar Mandilwar

Diwakar Mandilwar

Numerade Educator

Problem 107

You have the six pieces of metal listed below, plus a beaker of water containing $3.00 \times 10^{2} \mathrm{g}$ of water. The water temperature is $21.00^{\circ} \mathrm{C}$
$$\begin{array}{lcc}\text { Metals } & \text { Specific Heat }(\mathrm{J} / \mathrm{g} \mathrm{K}) & \text { Mass }(\mathrm{g}) \\\hline \text { 1. Al } & 0.9002 & 100.0 \\
\text { 2. Al } & 0.9002 & 50.0 \\\text { 3. Au } & 0.1289 & 100.0 \\\text { 4. Au } & 0.1289 & 50.0 \\5.2 \mathrm{n} & 0.3860 & 100.0 \\6.2 \mathrm{n} & 0.3860 & 50.0 \\\hline\end{array}$$
(a) In your first experiment you select one piece of metal and heat it to $100^{\circ} \mathrm{C},$ and then select a second piece of metal and cool it to $-10^{\circ} \mathrm{C}$. Both pieces of metal are then placed in the beaker of water and the temperatures equilibrated. You want to select two pieces of metal to use, such that the final temperature of the water is as high as possible. What piece of metal will you heat? What piece of metal will you cool? What is the final temperature of the water?
(b) The second experiment is done in the same way as the first. However, your goal now is to cause the temperature to change the least, that is, the final temperature should be be as near to $21.00^{\circ} \mathrm{C}$ as possible. What piece of metal will you heat? What piece of metal will you cool? What is the final temperature of the water?

Victor Salazar

Numerade Educator

Problem 108

In lab, you plan to carry out a calorimetry experiment to determine the $\Delta_{\mathrm{r}} H$ for the exothermic reaction of $\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{s})$ and $\mathrm{HCl}(\mathrm{aq}) .$ Predict how each of the fol-
lowing will affect the calculated value of $\Delta_{r} H .$ (The value calculated for $\Delta_{\mathrm{r}} H$ for this reaction is a negative value so choose your answer from the following: $\Delta_{r} H$ will be too low [that is, a larger negative value], $\Delta_{\mathrm{r}} H$ will be unaffected, $\Delta_{r} H$ will be too high $[$ that is, a smaller negative value. $]$ )
(a) You spill a little bit of the $\mathrm{Ca}(\mathrm{OH})_{2}$ on the benchtop before adding it to the calorimeter.
(b) Because of a miscalculation, you add an excess of HCl to the measured amount of $\mathrm{Ca}(\mathrm{OH})_{2}$ in the calorimeter.
(b) $\mathrm{Ca}(\mathrm{OH})_{2}$ readily absorbs water from the air. The $\mathrm{Ca}(\mathrm{OH})_{2}$ sample you weighed had been exposed to the air prior to weighing and had absorbed some water.
(c) After weighing out $\mathrm{Ca}(\mathrm{OH})_{2},$ the sample sat in an open beaker and absorbed water.
(d) You delay too long in recording the final temperature.
(e) The insulation in your coffee cup calorimeter was poor and so some energy as heat was lost to the surroundings during the experiment.
(e) You have ignored the fact that energy as heat also raised the temperature of the stirrer and the thermometer in your system.

Elham Kordzadeh

Elham Kordzadeh

Numerade Educator