Thermodynamics ❮ 133- The temperature increases when lithium sulfate,
Li 2 SO 4 , dissolves in water. Which of the follow-
ing conclusions may be related to this?
(A) Lithium sulfate is less soluble in hot water.
(B) The hydration energies of lithium ions and
sulfate ions are very low.
(C) The heat of solution for lithium sulfate is
endothermic.
(D) Lithium sulfate solutions are not ideal solu-
tions. - Calcium carbonate, CaCO 3 , decomposes when
heated according to the following reaction:
CaCO 3 (s) CaO(s) + CO 2 (g)
Increasing the temperature shifts the equilibrium
to the right. Which of the following is applicable
to this reaction?
(A) The reaction is faster at higher temperatures.
(B) The process is enthalpy and entropy driven.
(C) The process is enthalpy driven.
(D) The process is entropy driven.
- Which of the following combinations is true
when ethanol, C 2 H 5 OH, boils?
(A) ΔH > 0 and ΔS > 0
(B) ΔH = 0 and ΔS > 0
(C) ΔH > 0 and ΔS < 0
(D) ΔH < 0 and ΔS < 0
Use the following information to answer questions
20–23:
Xe(g) + 2 F 2 (g) XeF 4 (g) ΔHf° = - 262 kJ mol-^1The above reaction is the standard heat of formation
reaction for xenon tetrafluoride.
- For this reaction, what can be said about the
value of ΔS°?
(A) ΔS° is near zero.
(B) ΔS° is positive.
(C) ΔS° is negative.
(D) The reaction does not involve ΔS°.
21. This reaction is spontaneous under standard
conditions. What will happen to the value of ΔG
for this reaction when the temperature increases
if you assume ΔS is negative?
(A) ΔG will decrease.
(B) ΔG will increase.
(C) ΔG will remain the same.
(D) Only ΔHf° is important; ΔG does not matter.
22. What will happen to the value of K for this reac-
tion as the temperature increases? Assume that
ΔG for this reaction is increasing.
(A) K will decrease.
(B) K will increase.
(C) K will approach 1.
(D) K is a constant and will not change.
23. If you have a table of standard thermodynamic
values for the substances involved in the reaction,
how might the temperature at which the reaction
changes from spontaneous to nonspontaneous be
predicted?
(A) It is impossible to predict the temperature.
(B) The change will occur at 298 K (25°C).
(C) ΔG cannot change from spontaneous to non-
spontaneous.
(D) At this point, ΔG = 0, which leads to T =
ΔH/ΔS.
24. Both carbon monoxide, CO, and nitrogen, N 2 ,
have about the same molar mass (28 g mol-^1 ).
Both molecules have a triple bond between the
two atoms. At absolute zero, the entropy of
CO(s) is greater than 4 J mol-^1 K-^1 , and that
of N 2 (s) is 0 J mol-^1 K-^1. Why is the standard
entropy of CO(g) greater than that of N 2 (g)?
(A) CO is more disordered than N 2.
(B) The presence of carbon leads to greater
entropy.
(C) Oxygen is more electronegative than nitrogen.
(D) The triple bond in CO is polar, whereas the
triple bond in N 2 is nonpolar.