Chapter 18 Practice Test

Question 1

Which of the following is a nonspontaneous event?

Answer 1

a wheelbarrow being moved from one place to another

Question 2

Which of the following examples of a spontaneous reaction does not involve a chemical energy difference?

Answer 2

a glider (plane) landing on an airport runway

Question 3

Which of the following events involves a spontaneous reaction that does not include a change in energy?

Answer 3

releasing a gas into the atmosphere

Question 4

Suppose that, instead of having two connected bulbs, you have three connected bulbs. Assume that you start with the valve closed, add some gas molecules to one bulb, and then remove the valve. Which of the following shows the correct expression for the probability of finding all the gas molecules in one container after 1 hour?

Answer 4

probability = (1/3)x, where x = the number of molecules

Question 5

Look at the thermal energy drawing.

Which statement about this thermal energy event is not correct?

Answer 5

Heat moving into the house would violate the first law of thermodynamics.

Question 6

Which statement about enthalpy is not correct?

Answer 6

In a spontaneous reaction, the enthalpy change is always positive.

Question 7

The second law of thermodynamics says that the entropy of the universe tends to increase. In other words, the universe prefers maximum disorder. With respect to entropy, which statement is not correct?

Answer 7

The temperature does not affect the absolute entropy value.

Question 8

Look at the plot for entropy, (S°) vs. T (K).

Which statement about this plot is not correct?

Answer 8

There are two ranges in the plot where the temperature of the substance is simply increasing. The value for S° at any point in those ranges can be calculated using the formula

Question 9

Look at the plot for entropy versus temperature.

Which of the following describes Range B?

Answer 9

the entropy of fusion

Question 10

With respect to the third law of thermodynamics, which statement is not correct?

Answer 10

At 0 K for a substance, almost all of the thermal energy has been removed from the system

Question 11

Look at the diagram for the fusion of water (from liquid to solid).

Which statement about this diagram is not correct?

Answer 11

The value for ΔH changes much more than the value for TΔS as the temperature is lowered or raised.

Question 12

Look at the decomposition reaction for sodium bicarbonate
2NaHCO3(s) <==> Na2CO3(s) + H2O(g) + CO2(g)
Suppose that ΔH = 64.5 kJ/mol and ΔS = 0.167 kJ/mol*K. Which statement about this reaction is correct? Assume that ΔH and ΔS are constant for all the given temperatures

Answer 12

At about 386 K, the reaction is at equilibrium

Question 13

Which statement about a reaction in which liquid water freezes is not correct?

Answer 13

ΔS is positive.

Question 14

Calculate the standard free energy of formation of 2 mol of AgCl(s) at 25°C using the given information.

For Ag(s) at 25°C, S° = 42.55 J / mol • K and ΔH°f = 0.0 kJ / mol

For Cl2(g) at 25°C, S° = 222.96 J / mol • K and ΔH°f = 0.0 kJ / mol

For AgCl(s) at 25°C, S° = 96.2 J / mol • K and ΔH°f = −127.07 kJ / mol

Answer 14

−219.5 kJ / mol

Question 15

The value for ΔG° for the following reaction at 25°C is −394.4 kJ / mol.

C(s, graphite) + O2(g) <==> CO2(g)

Suppose that you raise the temperature to 108°C. What is ΔG° for the reaction at 108°C? (ΔH° = −393.5 kJ / mol and ΔS° = 2.83 J / mol • K)

Answer 15

−394.6 kJ / mol

Question 16

In the expression ΔG° f = ΔH – TΔS°, there is a value for absolute entropy, S°. Which statement about S° is not correct?

Answer 16

For some ions, the value for S° > 0. When these ions dissociate from the compound in aqueous solution, they “grab” H2O molecules and thus increase their S° value so that S° < 0, not > 0

Question 17

Which statement about the plots for lnKeq = −ΔH° / RT + ΔS° / R, in which ΔS° < 0, is correct?

Answer 17

For the endothermic reaction, the reactants are always favored.

Question 18

The expression ln (Keq ) = −ΔH° / RT + ΔS° / R relates the value of ΔG to the Keq term. Which statement about this expression for ln (Keq ) is not correct?

Answer 18

The value of ΔH° / RT increases with increasing temperature.

Question 19

Look at the diagram that shows ln (KEq ) = −ΔH° / RT + ΔS° / R for an endothermic reaction and an exothermic reaction where ΔS° < 0.

Which statement about this reaction is not correct?

Answer 19

By changing the temperature in the endothermic reaction where ΔS° < 0, we can influence whether products or reactants are favored at equilibrium.

Question 20

In this lesson, we investigated how temperature affects the value of Keq in the expression ln(Keq) = -ΔH°/RT + ΔS°/R. Which statement correctly states the effect of a temperature change on the value of Keq?

Answer 20

A temperature change only affects Keq through the -ΔH°/RT term

Question 21

Which of the following shows the correct van ’t Hoff equation?

Answer 21

ln (K2 / K1 ) = −(ΔH ° / R) (1 / T2 − 1 / T1 )

Question 22

Look at the plot for ΔS / R vs. 1 / T.

Which of the following statements is not correct?

Answer 22

There is a shift toward more product as you increase the temperature.

Question 23

Use the formula for ΔG to find ΔG for a reaction if ΔG° = 7.27 kJ / mol, T = 282 K, R = 8.31 × 10−3 kJ / mol • K, and Q = 0.67. Also, tell whether the reaction will shift toward the products or reactants to reach equilibrium.

Answer 23

ΔG = 6.33 kJ / mol; the system will shift toward the reactants to achieve equilibrium.

Question 24

What is the correct thermodynamic reaction quotient expression for the reaction?

CaCO3(s) <==> CaO(s) + CO2(g)

Answer 24

Q=PCO2

Question 25

What is ΔG for a reaction if ΔG° = 8.33 kJ / mol, T = 298 K, R = 8.31 × 10−3 kJ / mol • K, and Q = 0.23?

Answer 25

4.69 kJ / mol