LIU Chemistry Worksheet

Problem Set 5Answer the following questions on a separate sheet of paper. The questions must be done in the
order given. If you are skipping a question, leave space in case you decide to return to the problem. You
do not need to recopy the question, simply indicate its number in the upper left corner.
Do not type your answers. In most cases when the submission is typed blackboard will change the
formatting on your submission. Write your answers with blue or black ink. Then scan the document into
blackboard.
1. Explain why each of the following results in an increase in entropy.
a. Liquid methane become a gas.
b. Potassium nitrate being dissolved in water.
c. Confetti being released on New Year’s Eve.
2. A certain reaction has a enthalpy value of -157 kJ/mol and an entropy value of -97.6 J/mol K at
25.0℃.
a. Determine the Free Gibbs Energy in kJ/mol at 25.0℃.
b. Is the reaction spontaneous at 25.0℃?
c. Will this reaction be spontaneous at all possible Kelvin temperatures? Explain your answer.
3. The equilibrium constant for the reaction:
2SO2(g) + O2(g) ⇌ 2SO3(g)
is 2.8 x 102 at 25.0℃.
a. Determine the Free Gibb’s Energy in kJ/mol.
b. Using the data provided below, determine the enthalpy of reaction (kJ/mol) and entropy of
reaction (J/mol K)
Substance
SO2(g)
O2(g)
SO3(g)
°
-296.4
0
-395.2
∆𝐻𝑓 (kJ/mol)
°
S (J/Kmol)
248.5
205.0
256.2
c. Determine the entropy for the surroundings in J/mol K at 25.0℃.
d. Determine the entropy of the universe in J/mol K at 25.0℃.
e. Is the reaction spontaneous at 25.0℃? Explain your answer using the information calculated
in part a and part d.
4. For the reaction 2A(g) + B(g) → 4C + 3D, ∆G° is 456.2 kJ/mol at 25.0℃.
a. Write the Qc expression for this reaction.
b. Calculate the Qc when the concentration of [A] = 0.432 M, [B] = 1.234 M, [C] = 0.3367 M and
[D] = 0.250 M.
c. Calculate the nonstandard Free Gibbs Value in kJ/mol at 25.0℃
d. What should be done to the concentrations of C and D to make the reaction go from being
nonspontaneous to spontaneous? (Increase or decrease) Explain your answer. (Assume the
concentration of A and B remain at 0.432 M and 1.234 M)
5. State whether the sign of the entropy change expected for each of the following processes will
be positive or negative and explain your predictions.
a. 2NaOH(aq) + H2(g) → 2Na(s) + H2O(l)
b. I2(g) → 2I(g)
c. K2SO4(s) → 2K+(aq) + SO42-(aq)
6. Determine the boiling point in Celsius for CS2 given the following information.
Substance
CS2(g)
CS2(l)
°
115.3
87.3
∆𝐻𝑓 (kJ/mol)
°
S (J/molK)
237.8
151.0