CHEM 123 – University Chemistry Exam Pack 2024/2025 (Practice Exams with Detailed Answers and Explanations)

Chemistry 123 Practice
Exam Package




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content in CHEM 123.
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,1. What volume of air, measured at 22 °C and 745 mmHg, is required for the
complete combustion of 1.00 L of CH4(g) at 22 °C and 3.55 atm? (Air contains
20.95% O2(g) by volume).




2. CCl4, and important commercial solvent, is prepared by the reaction of Cl2(g)
with a carbon compound. Determine ΔH° for the reaction.

CS2(l) + 3Cl2(g) ⟶ CCl4(l) + S2Cl2(l)

Use appropriate data from the following listing:

CS2(l) + 3O2(g) ⟶ CO2(g) + 2SO2(g) ΔH° = -1077 kJ
2S(s) + Cl2(g) ⟶ S2Cl2(l) ΔH° = -58.2 kJ
C(s) + 2Cl2(g) ⟶ CCl4(l) ΔH° = -135.4 kJ
S(s) + O2(g) ⟶ SO2(g) ΔH° = -296.8 kJ
SO2(g) + Cl2(g) ⟶ SO2Cl2(l) ΔH° = +97.3 kJ
C(s) + O2(g) ⟶ CO2(g) ΔH° = -393.5 kJ
CCl4(l) + O2(g) ⟶ COCl2(g) + Cl2O(g) ΔH° = -5.2 kJ

,3. Indicate if the following statements are true or false:

a) All spontaneous processes must occur very rapidly.



b) The sum of q and w is a state function.



c) If a process has reached equilibrium, ΔSsystem must be zero.



d) For all spontaneous processes, under all conditions, ΔG must be
negative.



e) The absolute entropy of an element in its standard state must be zero.



4. Given the following data:

S(s) + 3/2O2(g) ⟶ SO3(g) ΔH° = -395.2 kJ
2SO2(s) + O2(g) ⟶ 2SO3(g) ΔH° = -198.2 kJ

Calculate ΔH° for the reaction:

S(s) + O2(g) ⟶ SO2(g)

, 5. Enthalpy is defined as:

a) The heat of combustion
b) The energy contained within a system
c) The sum of the internal energy and the pressure-volume product of a
system
d) The sum of the kinetic and potential energies
e) The work not limited to pressure-volume work

6. If for the reaction: CH4(g) + 2H2O(g) ⇌ CO2(g) + 4H2(g) where
ΔH° = +190 kJ, we add H2(g):

a) The reaction shifts to the right
b) The reaction shifts to the left
c) ΔH° increases
d) The temperature increases
e) There is no change in the equilibrium position

7. What is the effect of removing Fe3O4(s) from the reaction:

3Fe(s) + 4H2O(g) ⇌ Fe3O4(s) + 4H2(g)

a) The reaction shifts to the right
b) There is no change
c) The reaction shifts to the left
d) Kp is increased
e) Kp is decreased

8. According to Le Châtelier’s principle:

a) An increase in pressure always causes a change in the position of
equilibrium for any reaction.
b) The greatest yield of ammonia in the exothermic reaction
N2 + 3H2 ⇌ 2NH3 is attained at high temperature.
c) The equilibrium constant is increased for the reaction A + B ⇌ C if the
concentration of A is increased.
d) An increase of temperature causes a decrease in the value of the
equilibrium constant for an exothermic reaction.
e) When an equilibrium system is stressed, the system reacts to offset the
stress.