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

Define the terms system and surroundings. What does it mean to say that a system and its surroundings are in thermal equilibrium?

Arun Bana

Arun Bana

Numerade Educator

Problem 2

What determines the directionality of energy transfer as heat?

Breanna Kloczkowski

Breanna Kloczkowski

Numerade Educator

Problem 3

Identify whether the following processes are exothermic or endothermic.
(a) combustion of methane
(b) melting of ice
(c) raising the temperature of water from $25^{\circ} \mathrm{C}$ to $100^{\circ} \mathrm{C}$
(d) heating $\operatorname{CaCO}_{3}(\mathrm{s})$ to form $\mathrm{CaO}(\mathrm{s})$ and $\mathrm{CO}_{2}(\mathrm{g})$

Arun Bana

Numerade Educator

Problem 4

Identify whether the following processes are exothermic or endothermic.
(a) the reaction of $\mathrm{Na}(\mathrm{s})$ and $\mathrm{Cl}_{2}(\mathrm{g})$
(b) cooling and condensing gaseous $N_{2}$ to form liquid $\mathrm{N}_{2}$
(c) cooling a soft drink from $25^{\circ} \mathrm{C}$ to $0^{\circ} \mathrm{C}$
(d) heating $\mathrm{HgO}(\mathrm{s})$ to form $\mathrm{Hg}(\ell)$ and $\mathrm{O}_{2}(\mathrm{g})$

Arun Bana

Numerade Educator

Problem 5

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 6

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 $\mathrm{J} / \mathrm{mol} \cdot \mathrm{K}) ?$

Adam Wade

Numerade Educator

Problem 7

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

Breanna Kloczkowski

Breanna Kloczkowski

Numerade Educator

Problem 8

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

Arun Bana

Numerade Educator

Problem 9

The initial temperature of a 344 -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 10

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 11

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

Alice .

Numerade Educator

Problem 12

A 182 -g sample of gold at some temperature was added to 22.1 g of water. The initial water temperature was $25.0^{\circ} \mathrm{C},$ and the final temperature was $27.5^{\circ} \mathrm{C} .$ 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 sample?

Dr. Satish Ingale

Dr. Satish Ingale

Numerade Educator

Problem 13

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 14

When $108 \mathrm{g}$ 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 15

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 $45.0 \mathrm{g}$ of water at $25.0^{\circ} \mathrm{C} .$ When the water and metal came to thermal equilibrium, the temperature was $27.1^{\circ} \mathrm{C} .$ What is the specific heat capacity of zinc?

Alice .

Numerade Educator

Problem 16

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

Adam Wade

Numerade Educator

Problem 17

How much energy is evolved as heat when $1.0 \mathrm{L}$ 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 18

The energy required to melt $1.00 \mathrm{g}$ of ice at $0^{\circ} \mathrm{C}$ is 333 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 required to melt a tray of ice cubes to form liquid water at $0^{\circ} \mathrm{C} ?$

Bin Chen

Numerade Educator

Problem 19

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 20

Chloromethane, $\mathrm{CH}_{3} \mathrm{Cl}$, arises from microbial fermentation and is found throughout the environment. It is also produced industrially, 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 21

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 J/g $\cdot$ K and its heat of fusion is $11.4 \mathrm{J} / \mathrm{g} .$ )

Bin Chen

Numerade Educator

Problem 22

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 fusion of this metal is $59.2 \mathrm{J} / \mathrm{g} .$ )

Nishant Kumar

Numerade Educator

Problem 23

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 24

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 was given off as heat in this process? (The density of benzene is $0.80 \mathrm{g} / \mathrm{mL},$ its specific heat capacity is $1.74 \mathrm{J} / \mathrm{g} \cdot \mathrm{K}, \text { and its heat of fusion is } 127 \mathrm{J} / \mathrm{g} .)$

Jennifer Hudspeth

Jennifer Hudspeth

Numerade Educator

Problem 25

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. (EQUATION CAN'T COPY) Is this reaction endothermic or exothermic? What is the enthalpy change if $1.25 \mathrm{g}$ of $\mathrm{NO}$ is converted completely to NO $_{2} ?$

Ronald Prasad

Numerade Educator

Problem 26

Calcium carbide, $\mathrm{CaC}_{2}$, is manufactured by the reaction of CaO with carbon at a high temperature. (Calcium carbidCalcium 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.)e is then used to make acetylene.) $\begin{aligned} \mathrm{CaO}(\mathrm{s})+3 \mathrm{C}(\mathrm{s}) \rightarrow \mathrm{CaC}_{2}(\mathrm{s}) &+\mathrm{CO}(\mathrm{g}) \\ & \Delta_{\mathrm{r}} H^{\circ}=+464.8 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn} \end{aligned}$ 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 27

Isooctane ( 2,2,4 -trimethylpentane), one of the many hydrocarbons that make up gasoline, burns in air to give water and carbon dioxide. (EQUATION CAN'T COPY) What is the enthalpy change if you burn $1.00 \mathrm{L}$ of isooctane $(d=0.69 \mathrm{g} / \mathrm{mL}) ?$

Bin Chen

Numerade Educator

Problem 28

Acetic acid, $\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}$, is made industrially by the reaction of methanol and carbon monoxide. $\begin{aligned} \mathrm{CH}_{3} \mathrm{OH}(\ell)+\mathrm{CO}(\mathrm{g}) \rightarrow \mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}(\ell) & \\ \Delta_{\mathrm{r}} H^{\circ}=-134.6 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn} \end{aligned}$ What is the enthalpy change for producing $1.00 \mathrm{L}$ of acetic acid $(d=1.044 \mathrm{g} / \mathrm{mL})$ by this reaction?

Diwakar Mandilwar

Diwakar Mandilwar

Numerade Educator

Problem 29

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 30

You mix 125 mL of 0.250 M CsOH with 50.0 mL of $0.625 \mathrm{M}$ 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. $$ \mathrm{CsOH}(\mathrm{aq})+\mathrm{HF}(\mathrm{aq}) \rightarrow \mathrm{CsF}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell) $$

David Collins

Numerade Educator

Problem 31

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 32

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 $23.3^{\circ} \mathrm{C} .$ 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 33

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 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.) (IMAGE CAN'T COPY)

Alice .

Numerade Educator

Problem 34

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, $5.2 \mathrm{g}$ of concentrated $\mathrm{H}_{2} \mathrm{SO}_{4}(\ell)$ 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 $\mathrm{kJ} / \mathrm{mol}$

Bin Chen

Numerade Educator

Problem 35

Sulfur $(2.56 \mathrm{g})$ was burned in a constant volume calorimeter with excess $\mathrm{O}_{2}(\mathrm{g}) .$ The temperature increased 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 contained $815 \mathrm{g}$ of water. Calculate $\Delta U$ per mole of $\mathrm{SO}_{2}$ formed for the reaction $\mathrm{S}_{8}(\mathrm{s})+8 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 8 \mathrm{SO}_{2}(\mathrm{g})$ (IMAGE CAN'T COPY)

Bin Chen

Numerade Educator

Problem 36

Suppose you burned $0.300 \mathrm{g}$ of $\mathrm{C}(\mathrm{s})$ in an excess of $\mathrm{O}_{2}(\mathrm{g})$ in a constant volume calorimeter to give $\mathrm{CO}_{2}(\mathrm{g})$ $\mathrm{C}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{CO}_{2}(\mathrm{g})$ The temperature of the calorimeter, which contained 775 g of water, increased 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.

Bin Chen

Numerade Educator

Problem 37

Suppose you burned $1.500 \mathrm{g}$ of benzoic acid, $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CO}_{2} \mathrm{H},$ in a constant volume calorimeter and found that the temperature increased from $22.50^{\circ} \mathrm{C}$ to $31.69^{\circ} \mathrm{C} .$ The calorimeter contained $775 \mathrm{g}$ of water, and the bomb had a heat capacity of $893 \mathrm{J} / \mathrm{K}$. Calculate $\Delta U$ per mole of benzoic acid. (IMAGE CAN'T COPY)

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 38

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

Bin Chen

Numerade Educator

Problem 39

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 heated a 50.0 -g piece of silver to $99.8^{\circ} \mathrm{C}$ and then dropped it onto ice. When the metal's temperature had dropped to $0.0^{\circ} \mathrm{C},$ it is found that $3.54 \mathrm{g}$ of ice had melted. What is the specific heat capacity of silver?

Bin Chen

Numerade Educator

Problem 40

A $9.36-\mathrm{g}$ piece of platinum was heated to $98.6^{\circ} \mathrm{C}$ in a boiling water bath and then dropped onto ice. (See Study Question 39.) When the metal's temperature had dropped to $0.0^{\circ} \mathrm{C},$ it is found that $3.54 \mathrm{g}$ of ice had melted. What is the specific heat capacity of silver?

Amany Waheeb

Numerade Educator

Problem 41

The enthalpy changes for the following reactions can be measured: (EQUATIONS CAN'T COPY) (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.

Alice .

Numerade Educator

Problem 42

The enthalpy changes of the following reactions can be measured:
$$ \begin{aligned} \mathrm{C}_{2} \mathrm{H}_{4}(\mathrm{g})+3 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{CO}_{2}(\mathrm{g}) &+2 \mathrm{H}_{2} \mathrm{O}(\ell) \\
\Delta_{r} H^{\circ} &=-1411.1 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}
\end{aligned} $$ The enthalpy changes of the following reactions can be measured: $$ \begin{aligned} \mathrm{C}_{2} \mathrm{H}_{4}(\mathrm{g})+3 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{CO}_{2}(\mathrm{g}) &+2 \mathrm{H}_{2} \mathrm{O}(\ell) \\
\Delta_{r} H^{\circ} &=-1411.1 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}
\end{aligned} $$
(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 43

Enthalpy changes for the following reactions can be determined experimentally:
(EQUATIONS CAN'T COPY)
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). $$ 1 / 2 \mathrm{N}_{2}(\mathrm{g})+1 / 2 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{NO}(\mathrm{g}) \quad \Delta_{\mathrm{r}} H^{\circ}=? $$

Alice .

Numerade Educator

Problem 44

You wish to know the enthalpy change for the formation of liquid $\mathrm{PCl}_{3}$ 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 $\mathrm{PCl}_{5}(\mathrm{s}):$
$\begin{aligned} \mathrm{P}_{4}(\mathrm{s})+10 \mathrm{Cl}_{2}(\mathrm{g}) \rightarrow 4 \mathrm{PCl}_{5}(\mathrm{s}) & \\ \Delta_{r} H^{\circ} &=-1774.0 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn} \\ \mathrm{PCl}_{3}(\ell)+\mathrm{Cl}_{2}(\mathrm{g}) \rightarrow \mathrm{PCl}_{5}(\mathrm{s}) & \\ \Delta_{\mathrm{r}} H^{\circ} &=-123.8 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn} \end{aligned}$
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 45

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 46

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 47

(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 $\mathrm{L}$.)
(b) What is the 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 48

(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 $\Delta_{f} H^{\circ}$ 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?

Banhishikha Sinha

Banhishikha Sinha

Numerade Educator

Problem 49

Use standard enthalpies of formation in Appendix L to calculate enthalpy changes for the following:
(a) 1.0 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 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 50

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 51

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 is evolved or absorbed as heat in the oxidation of $10.0 \mathrm{g}$ of $\mathrm{NH}_{3} ?$

Bin Chen

Numerade Educator

Problem 52

The Romans used calcium oxide, $\mathrm{CaO},$ to produce a strong mortar to build stone structures. Calcium oxide 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 is evolved or absorbed as heat 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 53

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 54

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 55

The enthalpy change for the oxidation of naphthalene, $\mathrm{C}_{10} \mathrm{H}_{8},$ is measured by calorimetry. (EQUATION CAN'T COPY) 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 56

The enthalpy change for the oxidation of styrene, $\mathrm{C}_{8} \mathrm{H}_{8}$ is measured by calorimetry. $\begin{aligned} \mathrm{C}_{8} \mathrm{H}_{8}(\ell)+10 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 8 \mathrm{CO}_{2}(\mathrm{g}) &+4 \mathrm{H}_{2} \mathrm{O}(\ell) \\ \Delta_{\mathrm{r}} H^{\circ} &=-4395.0 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn} \end{aligned}$ 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 styrene, in $\mathrm{kJ} / \mathrm{mol}$.

Maryam Shahid

Numerade Educator

Problem 57

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 58

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 59

For each of the following, define a system and its surroundings, and give the direction of energy transfer between system and surroundings.
(a) Methane burns in a gas furnace in your home.
(b) Water drops, sitting on your skin after a swim, 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 60

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

Arun Bana

Numerade Educator

Problem 61

Use Appendix L to find the standard enthalpies of formation of oxygen atoms, oxygen molecules $\left(\mathrm{O}_{2}\right),$ 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 mol of $\mathrm{O}_{3}$ from $\mathrm{O}_{2} ?$

Alice .

Numerade Educator

Problem 62

You have a large balloon containing 1.0 mol of gaseous water vapor at $80^{\circ} \mathrm{C} .$ How will each step affect the internal energy of the system?
(a) The temperature of the system is raised to $90^{\circ} \mathrm{C}$
(b) The vapor is condensed to a liquid, at $40^{\circ} \mathrm{C}$

Bin Chen

Numerade Educator

Problem 63

Determine whether energy as heat is evolved or required, and whether work was done on the system or whether the system does work on the surroundings, in the following processes at constant pressure:
(a) Liquid water at $100^{\circ} \mathrm{C}$ is converted to steam at $100^{\circ} \mathrm{C}$
(b) Dry ice, $\mathrm{CO}_{2}(\mathrm{s}),$ sublimes to give $\mathrm{CO}_{2}(\mathrm{g})$

Arun Bana

Numerade Educator

Problem 64

Determine whether energy as heat is evolved or required, and whether work was done on the system or whether the system does work on the surroundings, in the following processes at constant pressure:
(a) Ozone, $\mathrm{O}_{3},$ decomposes to form $\mathrm{O}_{2}$
(b) Methane burns: $\mathrm{CH}_{4}(\mathrm{g})+2 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{CO}_{2}(\mathrm{g})+2 \mathrm{H}_{2} \mathrm{O}(\ell)$

Maryam Shahid

Numerade Educator

Problem 65

Use standard enthalpies of formation to calculate the enthalpy change that occurs when $1.00 \mathrm{g}$ of $\mathrm{SnCl}_{4}(\ell)$ reacts with excess $\mathrm{H}_{2} \mathrm{O}(\ell)$ to form $\mathrm{SnO}_{2}(\mathrm{s})$ and $\mathrm{HCl}(\mathrm{aq})$

Bin Chen

Numerade Educator

Problem 66

Which evolves more energy on cooling from $50^{\circ} \mathrm{C}$ to $10^{\circ} \mathrm{C}: 50.0 \mathrm{g}$ of water or $100 .$ g of ethanol $\left(C_{\text {ethanol }}=\right.$ $2.46 \mathrm{J} / \mathrm{g} \cdot \mathrm{K}) ?$

Bin Chen

Numerade Educator

Problem 67

You determine that 187 J of energy as 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?

Bin Chen

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 enthalpy of fusion of ice at $0^{\circ} \mathrm{C}$ is $333 \mathrm{J} / \mathrm{g}$; the enthalpy of vaporization of liquid water at $100^{\circ} \mathrm{C}$ is $2256 \mathrm{J} / \mathrm{g}.$

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 reaches thermal equilibrium at $0^{\circ} \mathrm{C},$ how much ice has melted?

Bin Chen

Numerade Educator

Problem 70

Three 45 -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
$240 \mathrm{mL}$ 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

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.
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.
(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 exo-or endothermic?

Banhishikha Sinha

Banhishikha Sinha

Numerade Educator

Problem 74

Chloromethane, $\mathrm{CH}_{3} \mathrm{Cl}$, a compound found throughout the environment, is formed in the reaction of chlorine atoms with methane. Chloromethane, $\mathrm{CH}_{3} \mathrm{Cl}$, a compound found throughout the environment, is formed in the reaction of chlorine atoms with methane. (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 $\mathrm{HCl}(\mathrm{g})$ Is the reaction exo- or endothermic?
(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 starting place 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 exo- or endothermic?
(c) What is the enthalpy change if $1000.0 \mathrm{kg}$ (1 metric ton) 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 $\left[\mathrm{C}_{4} \mathrm{H}_{10}(\mathrm{g}), \Delta_{3} H^{\circ}=-127.1 \mathrm{kJ} / / \mathrm{mol}\right],$ gasoline, or ethanol $\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right) .$ Calculate the enthalpy of combustion per gram of each of these fuels. [Assume that gasoline is represented by isooctane, $\mathrm{C}_{8} \mathrm{H}_{18}(\ell),$ with $\Delta_{f} H^{\circ}=$ $-259.3 \mathrm{kJ} / \mathrm{mol.}]$ Do you notice any great differences emong these fuels? How are these differences related to their composition? (IMAGE CAN'T 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 $\mathrm{C}_{8} \mathrm{H}_{18}$ (isooctane), the latter being representative of the compounds in gasoline. $\left(\Delta_{j} H^{\circ}=-259.2 \mathrm{kJ} / \mathrm{mol}$ 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 $\mathrm{N}_{2} \mathrm{H}_{2}\left(\mathrm{CH}_{3}\right)_{2}(\ell)+4 \mathrm{O}_{2}(\mathrm{g}) \rightarrow$ 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. (IMAGE CAN'T COPY)

Bin Chen

Numerade Educator

Problem 79

(a) Calculate the enthalpy change, $\Delta_{\mathrm{r}} H^{\circ}$, for the formation of 1.00 mol of strontium carbonate (the material that gives the red color in fireworks) from its elements.
$$ \mathrm{Sr}(\mathrm{s})+\mathrm{C}(\mathrm{s})+3 / 2 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{SrCO}_{3}(\mathrm{s}) $$(EQUATIONS CAN'T COPY) (b) Draw an energy level diagram relating the energy quantities in this problem.

Victor Salazar

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? (1 Calone $=1000 \mathrm{kCal}=4184 \mathrm{J} .$ )
(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

Chloroform, CHCl $_{3},$ is formed from methane and schlorine 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 $\Delta_{r} H^{\circ},$ 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 enthalpy changes for the following reactions: Calculate $\Delta_{r} H^{\circ},$ 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 enthalpy changes for the following reactions:

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 Study 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 -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 was the final temperature of the copper and water after thermal equilibrium was reached? $\left(C_{\mathrm{Cu}}=0.385 \mathrm{J} / \mathrm{g} \cdot \mathrm{K}\right)$

Bin Chen

Numerade Educator

Problem 85

Insoluble $\mathrm{AgCl}(\mathrm{s})$ precipitates when solutions of $\mathrm{AgNO}_{3}(\mathrm{aq})$ and $\mathrm{NaCl}(\mathrm{aq})$ are mixed. $\mathrm{AgNO}_{3}(\mathrm{aq})+\mathrm{NaCl}(\mathrm{aq}) \rightarrow \mathrm{AgCl}(\mathrm{s})+\mathrm{NaNO}_{3}(\mathrm{aq})$ $$ \Delta_{\mathrm{r}} H^{\circ}=? $$ 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 AgCl(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.
$\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})+2 \mathrm{NaBr}(\mathrm{aq}) \rightarrow \mathrm{PbBr}_{2}(\mathrm{s})+2 \mathrm{NaNO}_{3}(\mathrm{aq})$ $$ \Delta_{\mathrm{r}} H^{\circ}=? $$ To measure the enthalpy change, $200 .$ mL of $0.75 \mathrm{M}$ $\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})$ and $200 . \mathrm{mL}$ 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 $\mathrm{k} \mathrm{J} / \mathrm{mol}$. (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 $\Delta U$ for 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 $\mathrm{kJ} / \mathrm{mol}$ ? (IMAGE CAN'T COPY)

Bin Chen

Numerade Educator

Problem 88

A bomb calorimetric experiment was run to determine the enthalpy of combustion of ethanol. 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 $$ \mathrm{Mg}(\mathrm{s})+2 \mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow \mathrm{Mg}(\mathrm{OH})_{2}(\mathrm{s})+\mathrm{H}_{2}(\mathrm{g}) $$ (IMAGE CAN'T COPY) 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 $85^{\circ} \mathrm{C} ?$

Bin Chen

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. $$ 4 \mathrm{Fe}(\mathrm{s})+3 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{Fe}_{2} \mathrm{O}_{3}(\mathrm{s}) $$ (IMAGE CAN'T COPY) 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 $37^{\circ} \mathrm{C} ?$

Bin Chen

Numerade Educator

Problem 91

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

Arun Bana

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

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

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 5.4 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? (TABLE CAN'T COPY)

Pam Owens

Numerade Educator

Problem 95

Observe the molar heat capacity values for the metals in Figure $5.4 .$ 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

You are attending summer school and 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. 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?

Arun Bana

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 $2800 \mathrm{ft}^{2}$ ) of floor area and that the ceilings are 2.50 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: $\mathrm{CaBr}_{2}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \rightarrow \mathrm{CaO}(\mathrm{s})+2 \mathrm{HBr}(\mathrm{g})$ $\begin{aligned} \mathrm{Hg}(\ell)+2 \mathrm{HBr}(\mathrm{g}) & \rightarrow \mathrm{HgBr}_{2}(\mathrm{s})+\mathrm{H}_{2}(\mathrm{g}) \\ \mathrm{HgBr}_{2}(\mathrm{s})+\mathrm{CaO}(\mathrm{s}) & \rightarrow \mathrm{HgO}(\mathrm{s})+\mathrm{CaBr}_{2}(\mathrm{s}) \end{aligned}$ $$\begin{aligned}
\mathrm{Hg}(\ell)+2 \mathrm{HBr}(\mathrm{g}) & \rightarrow \mathrm{HgBr}_{2}(\mathrm{s})+\mathrm{H}_{2}(\mathrm{g}) \\
\mathrm{HgBr}_{2}(\mathrm{s})+\mathrm{CaO}(\mathrm{s}) & \rightarrow \mathrm{HgO}(\mathrm{s})+\mathrm{CaBr}_{2}(\mathrm{s})
\end{aligned}$$(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 exo- or endothermic? $\Delta_{f} H^{\circ}\left[\operatorname{CaBr}_{2}(\mathrm{s})\right]=-683.2 \mathrm{kJ} / \mathrm{mol}$ $\Delta_{f} H^{\circ}\left[\mathrm{HgBr}_{2}(\mathrm{s})\right]=-169.5 \mathrm{kJ} / \mathrm{mol}$ (d) 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 $(2.54 \mathrm{cm})$ of rain falls over a square mile of ground $\left(2.59 \times 10^{6} \mathrm{m}^{2}\right) .$ (Density of water is $1.0 \mathrm{g} / \mathrm{cm}^{3} .$ ) The enthalpy of vaporization of water at $25^{\circ} \mathrm{C}$ is $44.0 \mathrm{kJ} /$ mol. How much energy is transferred as heat 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 $(250 \mathrm{mL}$ 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 $-960 \mathrm{kJ}$ (IMAGE CAN'T 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 as follows: (TABLE CAN'T COPY)
(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 $\mathrm{H}_{2} \mathrm{O}(\ell)$
(b) Use the $\Delta_{c} H^{\circ}$ data in part (a), along with the enthalpies of formation of $\mathrm{CO}_{2}(\mathrm{g})$ and $\mathrm{H}_{2} \mathrm{O}(\ell)$ 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? (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 $\mathrm{H}_{2} \mathrm{O}(\ell)$
(b) Use the $\Delta_{c} H^{\circ}$ data in part (a), along with the enthalpies of formation of $\mathrm{CO}_{2}(\mathrm{g})$ and $\mathrm{H}_{2} \mathrm{O}(\ell)$ 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?
(IMAGE CAN'T 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 dissociation enthalpy.)
(TABLE CAN'T COPY) (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 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?

Kevin Zaborsky

Numerade Educator

Problem 103

When 0.850 g of Mg was burned in oxygen in a constant volume calorimeter, $25.4 \mathrm{kJ}$ of energy as heat was evolved. The calorimeter was in an insulated container with $750 . \mathrm{g}$ of water at an initial temperature of $18 . \overline{6}^{\circ} \mathrm{C}$. The heat capacity of the bomb in the calorimeter is $820 . \mathrm{J} / \mathrm{K}$
(a) Calculate $\Delta U$ for the oxidation of $\mathrm{Mg}$ (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 $\left(10.0 \mathrm{g}, C_{\mathrm{Au}}=0.129 \mathrm{J} / \mathrm{g} \cdot \mathrm{K}\right)$ is heated to $100.0^{\circ} \mathrm{C} .$ A piece of copper (also $10.0 \mathrm{g}$, $\left.C_{\mathrm{Cu}}=0.385 \mathrm{J} / \mathrm{g} \cdot \mathrm{K}\right)$ is chilled in an ice bath to $0^{\circ} \mathrm{C}$ Both pieces of metal are placed in a beaker containing $150 . \mathrm{g} \mathrm{H}_{2} \mathrm{O}$ 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.) (GRAPH CAN'T COPY) (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 by reaction with $\mathrm{O}_{2}(\mathrm{g}) ?$
(d) Each arrow on the diagram represents a chemical reaction. Write the equation for the reaction that converts methane to methanol.

Victor Salazar

Numerade Educator

Problem 106

Calculate $\Delta_{\mathrm{r}} H^{\mathrm{o}}$ 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.
(EQUATIONS CAN'T COPY)

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 $21.00^{\circ} \mathrm{C}$. (TABLE CAN'T COPY) (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 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 tempera-

Victor Salazar

Numerade Educator

Problem 108

In lab, you plan to carry out a calorimetry experiment to determine $\Delta_{\mathrm{r}} H$ for the exothermic reaction of $\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{s})$ and $\mathrm{HCl}(\mathrm{aq}) .$ Predict how each of the following will affect the calculated value of $\Delta_{\mathrm{r}} H$. (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, $\Delta_{\mathrm{r}} H$ 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.
(c) $\mathrm{Ca}(\mathrm{OH})_{2}$ 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.
(d) After weighing out $\mathrm{Ca}(\mathrm{OH})_{2},$ the sample sat in an open beaker and absorbed water.
(e) You delay too long in recording the final temperature.
(f) The insulation in your coffee-cup calorimeter was poor, so some energy as heat was lost to the surroundings during the experiment.
(g) 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

Problem 109

Sublimation of $1.0 \mathrm{g}$ of dry ice, $\mathrm{CO}_{2}(\mathrm{s}),$ forms $0.36 \mathrm{L}$ of $\mathrm{CO}_{2}(\mathrm{g})$ (at $-78^{\circ} \mathrm{C}$ and 1 atm pressure). The expanding gas can do work on the surroundings. Calculate the amount of work done on the surroundings using the equation $w=-P \times \Delta V$ (Note: $L \times$ atm is a unit of energy; 1 L atm $=101.3 \mathrm{J}$.)

Bin Chen

Numerade Educator

Problem 110

In the reaction of two moles of gaseous hydrogen and one mole of gaseous oxygen to form two moles of gaseous water vapor, two moles of products are formed from 3 moles of reactants. If this reaction is done at $\left.1.0 \text { atm pressure (and at } 0^{\circ} \mathrm{C}\right),$ the volume is reduced by $22.4 \mathrm{L}$ (a) In this reaction, how much work is done on the system $\left(\mathrm{H}_{2}, \mathrm{O}_{2}, \mathrm{H}_{2} \mathrm{O}\right)$ by the surroundings?
(b) The enthalpy change for this reaction is $-483.6 \mathrm{kJ}$ Use this value, along with the answer to (a), to calculate $\Delta_{r} U$, the change in internal energy in the system.

Arun Bana

Numerade Educator