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Holt Chemistry

R.Thomas Myers, Keith Oldham,Savatore Tocci

Chapter 10

Causes of Change

Educators


Problem 1

What is dependent on the average kinetic
energy of the atoms in a substance?

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Problem 2

Define heat.

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Problem 3

Name a device used for measuring
enthalpy changes.

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Problem 4

What is a spontaneous reaction?

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Problem 5

What is entropy?

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Problem 6

Define Gibbs energy, and explain its
usefulness.

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Problem 7

Distinguish between heat and temperature.

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Problem 8

How can you tell which one of two samples
will release energy in the form of heat when
the two samples are in contact?

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Problem 9

What is molar heat capacity, and how can it
be measured?

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Problem 10

What is molar enthalpy change?

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Problem 11

What influences the changes in molar
enthalpy?

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Problem 12

Name two processes for which you could
determine an enthalpy change.

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Problem 13

Explain the meanings of $H, \Delta H,$ and $\Delta H_{f}^{o}$

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Problem 14

State Hess's law. How is it used?

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Problem 15

Which thermodynamic property of a food
is of interest to nutritionists? Why?

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Problem 16

What is adiabatic calorimetry?

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Problem 17

Why is entropy described as an extensive
property?

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Problem 18

Explain how a comprehensive table of
standard Gibbs energies of formation can
be used to determine the spontaneity
of any chemical reaction.

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Problem 19

What information is needed to be certain
that a chemical reaction is nonspontaneous?

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Problem 20

You need 70.2 $\mathrm{J}$ to raise the temperature of
34.0 $\mathrm{g}$ of ammonia, $\mathrm{NH}_{3}(g),$ from $23.0^{\circ} \mathrm{C}$ to
$24.0^{\circ} \mathrm{C}$ . Calculate the molar heat capacity
of ammonia.

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Problem 21

Calculate $C$ for indium metal given that
1.0 mol In absorbs 53 J during the following
process.
$$\operatorname{In}(s, 297.5 \mathrm{K}) \longrightarrow \operatorname{In}(s, 299.5 \mathrm{K})$$

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Problem 22

Calculate $\Delta H$ when 1.0 mol of nitrogen is
heated from 233 $\mathrm{K}$ to 475 $\mathrm{K}$ .

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Problem 23

What is the change in enthalpy when 11.0 $\mathrm{g}$
of liquid mercury is heated by $15^{\circ} \mathrm{C}$ ?

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Problem 24

Calculate $\Delta H$ when 1.0 $\mathrm{mol}$ of argon is
cooled from 475 $\mathrm{K}$ to 233 $\mathrm{K}$

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Problem 25

What enthalpy change occurs when 112.0 $\mathrm{g}$
of barium chloride experiences a change of
temperature from $15^{\circ} \mathrm{C}$ to $-30^{\circ} \mathrm{C}$ .

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Problem 26

The diagram below represents an interpretation of Hess's law for the following reaction.
$$\mathrm{Sn}(s)+2 \mathrm{Cl}_{2}(g) \rightarrow \mathrm{SnCl}_{4}(l)$$
Use the diagram to determine $\Delta H$ for each
step and the net reaction.
\begin{equation}
\begin{array}{ll}{\mathrm{Sn}(s)+\mathrm{Cl}_{2}(g) \rightarrow \mathrm{SnCl}_{2}(l)} & {\Delta H=?} \\ {\mathrm{SnCl}_{2}(s)+\mathrm{Cl}_{2}(g) \rightarrow \mathrm{SnCl}_{4}(l)} & {\Delta H=?} \\ {\mathrm{Sn}(s)+2 \mathrm{Cl}_{2}(g) \rightarrow \operatorname{SnCl}_{4}(l)} & {\Delta H=?}\end{array}
\end{equation}

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Problem 27

Use tabulated values of standard enthalpies
of formation to calculate the enthalpy
change accompanying the reaction
$4 \mathrm{Al}(s)+6 \mathrm{H}_{2} \mathrm{O}(l) \rightarrow 2 \mathrm{Al}_{2} \mathrm{O}_{3}(s)+6 \mathrm{H}_{2}(g)$
Is the reaction exothermic?

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Problem 28

The reaction $2 \mathrm{Fe}_{2} \mathrm{O}_{3}(s)+3 \mathrm{C}(s) \rightarrow 4 \mathrm{Fe}(s)+$
3 $\mathrm{CO}_{2}(g)$ is involved in the smelting of iron.
Use $\Delta H_{f}^{o}$ values to calculate the enthalpy
change during the production of 1 $\mathrm{mol}$
of iron.

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Problem 29

For glucose, $\Delta H_{f}^{o}=-1263 \mathrm{kJ} / \mathrm{mol} .$ Calculate
the enthalpy change when 1 $\mathrm{mol}$ of
$\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(s)$ combusts to form $\mathrm{CO}_{2}(g)$ and
$\mathrm{H}_{2} \mathrm{O}(l) .$

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Problem 30

Given the entropy change for the first two
reactions below, calculate the entropy
change for the third reaction below.
\begin{equation}
\begin{array}{c}{\mathrm{S}_{8}(s)+8 \mathrm{O}_{2}(g) \rightarrow 8 \mathrm{SO}_{2}(g) \Delta S=89 \mathrm{J} / \mathrm{K}} \\ {2 \mathrm{SO}_{2}(s)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{SO}_{3}(g) \Delta S=-188 \mathrm{J} / \mathrm{K}} \\ {\mathrm{S}_{8}(s)+12 \mathrm{O}_{2}(g) \rightarrow 8 \mathrm{SO}_{3}(g) \Delta S=?}\end{array}
\end{equation}

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Problem 31

$.$ The standard entropies for the following
substances are 26.9 $\mathrm{J} / \mathrm{K} \bullet$ mol for $\mathrm{MgO}(s)$
213.8 $\mathrm{J} / \mathrm{K} \bullet \mathrm{mol}$ for $\mathrm{CO}_{2}(g),$ and
65.7 $\mathrm{J} / \mathrm{K} \bullet \mathrm{mol}$ for $\mathrm{MgCO}_{3}(s) .$ Determine
the entropy for the reaction below.
$$
\mathrm{MgCO}_{3}(s) \rightarrow \mathrm{MgO}(s)+\mathrm{CO}_{2}(g)
$$

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Problem 32

A reaction has $\Delta H=-356 \mathrm{kJ}$ and $\Delta S=-36$
$\mathrm{J} / \mathrm{K} .$ Calculate $\Delta G$ at $25^{\circ} \mathrm{C}$ to confirm that
the reaction is spontaneous.

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Problem 33

A reaction has $\Delta H=98 \mathrm{kJ}$ and $\Delta S=292 \mathrm{J} / \mathrm{K}$ .
Investigate the spontaneity of the reaction at
room temperature. Would increasing the
temperature have any effect on the
spontaneity of the reaction?

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Problem 34

The sugars glucose, $\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(a q),$ and
sucrose, $\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}(a q),$ have $\Delta G_{f}^{\prime}$ values of
$-915 \mathrm{kJ}$ and $-1551 \mathrm{kJ}$ respectively. Is the
hydrolysis reaction, $\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}(a q)+$
$\mathrm{H}_{2} \mathrm{O}(l) \rightarrow 2 \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(a q),$ likely to occur $?$

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Problem 35

How are the coefficients in a chemical
equation used to determine the change in a
thermodynamic property during a chemical
reaction?

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Problem 36

Is the following reaction exothermic? The
standard enthalpy of formation for
$\mathrm{CH}_{2} \mathrm{O}(g)$ is approximately $-109 \mathrm{kJ} / \mathrm{mol}$ .
$$\mathrm{CH}_{2} \mathrm{O}(g)+\mathrm{CO}_{2}(g) \rightarrow \mathrm{H}_{2} \mathrm{O}(g)+2 \mathrm{CO}(g)$$

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Problem 37

Predict whether $\Delta S$ is positive or negative
for the following reaction.
$$\mathrm{Ag}^{+}(a q)+\mathrm{Cl}^{-}(a q) \rightarrow \mathrm{AgCl}(s)$$

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Problem 38

Explain why $\mathrm{AlCl}_{3}$ has a molar heat
capacity that is approximately four times the
molar heat capacity of a metallic crystal.

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Problem 39

At high temperatures, does enthalpy or
entropy have a greater effect on a reaction's
Gibbs energy?

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Problem 40

Calculate the enthalpy of formation for
sulfur dioxide, $\mathrm{SO}_{2},$ from its elements, sulfur
and oxygen. Use the balanced chemical
equation and the following information.
\begin{equation}
\begin{array}{c}{\mathrm{S}(s)+\frac{3}{2} \mathrm{O}_{2}(g) \rightarrow \mathrm{SO}_{3}(g) \quad \Delta H=-395.8 \mathrm{kJ} / \mathrm{mol}} \\ {2 \mathrm{SO}_{2}(g)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{SO}_{3}(g) \quad \Delta H=-198.2 \mathrm{kJ} / \mathrm{mol}}\end{array}
\end{equation}

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Problem 41

Using the following values, compute the $\Delta G$
value for each reaction and predict whether
they will occur spontaneously.

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Problem 42

Hydrogen gas can be prepared for use in
cars in several ways, such as by the decomposition of water or hydrogen chloride.
$$\begin{array}{l}{2 \mathrm{H}_{2} \mathrm{O}(l) \rightarrow 2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g)} \\ {2 \mathrm{HCl}(g) \rightarrow \mathrm{H}_{2}(g)+\mathrm{Cl}_{2}(g)}\end{array}$$
Use the following data to determine whether
these reactions can occur spontaneously at
$25^{\circ} \mathrm{C}$ . Assume that $\Delta H$ and $\Delta S$ are constant.

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Problem 43

Why are the specific heats of $\mathrm{F}_{2}(g)$ and
$\mathrm{Br}_{2}(g)$ very different, whereas their molar
heat capacities are very similar?

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Problem 44

Look at the two pictures below this
question. Which picture appears to have
more order? Why? Are there any
similarities between the order of marbles
and the entropy of particles?

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Problem 45

Why must nutritionists make corrections to
bomb calorimetric data if a food contains
cellulose or other indigestible fibers?

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Problem 46

Give examples of situations in which (a) the
entropy is low; (b) the entropy is high.

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Problem 47

Design an experiment to measure the
molar heat capacities of zinc and copper.
If your teacher approves the design, obtain
the materials needed and conduct the
experiment. When you are finished, com-
pare your experimental values with those
rom a chemical handbook or other
reference source.

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Problem 48

Use the following terms to create a concept
map: calorimeter, enthalpy, entropy, Gibbs
energy, and Hesss's Law

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Problem 49

How would the slope differ if you were to
cool the water at the same rate that graph
shows the water was heated?

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Problem 50

What would a slope of zero indicate about
the temperature of water during heating?

Matthew L.
Numerade Educator

Problem 51

Calculate the slope given the following data.
$$\begin{array}{ll}{y_{2}=3.3 \mathrm{K}} & {x_{2}=50 \mathrm{s}} \\ {y_{1}=5.6 \mathrm{K}} & {x_{1}=30 \mathrm{s}}\end{array}$$

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Problem 52

Calculate the slope given the following data.
$$\begin{array}{ll}{y_{2}=63.7 \mathrm{mL}} & {x_{2}=5 \mathrm{s}} \\ {y_{1}=43.5 \mathrm{mL}} & {x_{1}=2 \mathrm{s}}\end{array}$$

Matthew L.
Numerade Educator

Problem 53

Graphing Calculator
Calculating the Gibbs-Energy Change

The graphing calculator can run a program
that calculates the Gibbs-energy change,
given the temperature, $T$ , change in enthalpy
$\Delta H,$ and change in entropy, $\Delta S .$ Given that
the temperature is 298 $\mathrm{K}$ , the change in
enthalpy is 131.3 $\mathrm{kJ} / \mathrm{mol}$ , and the change in
entropy is $0.134 \mathrm{kJ} /(\mathrm{mol} \cdot \mathrm{K}),$ you can calculate Gibbs-energy change in kilojoules per
mole. Then use the program to make calculations.

Go to Appendix C. If you are using a TI-83
Plus, you can download the program
ENERGY data and run the application
as directed. If you are using another

calculator, your teacher will provide you with
keystrokes and data sets to use. After you
have run the program, answer the following
questions.

\begin{equation}
\begin{array}{l}{\text { a. What is the Gibbs-energy change given a }} \\ {\text { temperature of } 300 \mathrm{K}, \text { a change in enthalpy }} \\ {\text { of } 132 \mathrm{kJ} / \mathrm{mol} \text { and a change in entropy of }} \\ {0.086 \mathrm{kJ} / /(\mathrm{mol} \cdot \mathrm{K}) ?}\\{\text { b. What is the Gibbs-energy change given a }} \\ {\text { temperature of } 288 \mathrm{K}, \text { a change in enthalpy }} \\ {\text { of } 115 \mathrm{kJ} / \mathrm{mol} \text { and a change in entropy of }} \\ {0.113 \mathrm{kJ} /(\mathrm{mol} \cdot \mathrm{K}) ?}\\{\text { c. What is the Gibbs-energy change given a }} \\ {\text { temperature of } 298 \mathrm{K} \text { , a change in enthalpy }} \\ {\text { of } 181 \mathrm{kJ} / \mathrm{mol} \text { and a change in entropy of }} \\ {0.135 \mathrm{kJ} /(\mathrm{mol} \cdot \mathrm{K}) ?}\end{array}
\end{equation}

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