Thermodynamics practice problems focus on entropy, free energy, and spontaneity in chemical reactions. This resource is designed for chemistry students preparing for exams, covering key concepts such as ΔG, ΔH, and ΔS calculations. It includes a variety of practice questions that challenge students to evaluate standard molar entropy and predict reaction spontaneity. Ideal for those studying for AP Chemistry or university-level thermodynamics courses, this practice set enhances understanding of thermodynamic principles and their applications in real-world scenarios.

Key Points

  • Includes practice problems on entropy and free energy calculations.
  • Covers concepts of spontaneity and thermodynamic principles.
  • Features questions on evaluating standard molar entropy for various substances.
  • Designed for AP Chemistry students and undergraduate chemistry courses.
Aine Lee
7 pages
Exams
Aine Lee
7 pages
Exams
185
/ 7
1
General Chemistry II Jasperse
Entropy, Spontaneity, and Free Energy. Extra Practice Problems
General Types/Groups of problems:
Evaluating Relative Molar Entropy for Chemicals
p1
Calculating ΔG for Reactions (Math)
p5
Evaluating ΔS for Reactions (non-math)
p2
ΔG, ΔH, ΔS, Equilibrium, and Temperature
p6
Calculating ΔS for Reactions (Math)
p2
Answers
p7
Entropy/Enthalpy and Spontaneity.
p4
Key Equations Given for Test:
For weak acids alone in water:
[H
+
] =
€
K
a
x WA
[ ]
€
K
b
x WB
[ ]
pZ= -logZ
General definition for p of anything
[H
+
][HO
-
] = 1.00 x 10
-14
For Buffer: pH = pK
a
+ log[base]/[acid]
Henderson-Hasselbalch Equation
∆G˚ = G˚ (products) – G˚ (reactants)
EVALUATING/RANKING STANDARD MOLAR ENTROPY (S°) FOR CHEMICALS (non-math)
1. Which of the following is in the correct order of standard state entropy?
I.
Liquid water < gaseous water
II.
Liquid water < solid water
III.
NH
3
< H
2
a.
I only
d.
I and II only
b.
II only
e.
I and III only
c.
III only
2. Which of the following will have the greatest standard molar entropy (S°)?
a.
NH
3
(g)
d.
H
2
O(l)
b.
He(g)
e.
CaCO
3
(s)
c.
C(s, graphite)
3. Indicate which of the following has the lowest standard molar entropy (S°).
a.
CH
4
(g)
d.
Na(s)
b.
CH
3
CH
2
OH()
e.
He(g)
c.
H
2
O(s)
4. Indicate which of the following has the highest entropy at 298 K.
a.
0.5 g of HCN
b.
1 mol of HCN
c.
2 kg of HCN
d.
2 mol of HCN
e.
All of the above have the same entropy at 298 K.
2
EVALUATING ΔS FOR REACTIONS (non-math recognition)
5. Indicate which one of the following reactions result in a positive ΔS
sys
.
a.
AgNO
3
(aq) + NaCl(aq) D AgCl(s) + NaNO
3
(aq)
b.
H
2
O (g) + CO
2
(g) D H
2
CO
3
(aq)
c.
H
2
(g) + I
2
(g) D 2
Hl(g)
d.
C
2
H
2
O
2
(g) D 2
CO(g) + H
2
(g)
e.
H
2
O(g) D H
2
O(l)
6. Indicate which one of the following reactions results in a negative ΔS
sys
.
a.
H
2
O(g) D H
2
O(s)
b.
CaCO
3
(s) D CaO(s) + CO
2
(g)
c.
CuSO
4
(H
2
O)
5
(s) D CuSO
4
(s) + 5H
2
O(g)
d.
14O
2
(g) + 3NH
4
NO
3
(s) + C
10
H
22
(l) → 3N
2
(g) + 17H
2
O(g) + 10CO
2
(g)
e.
CO
2
(aq) D CO
2
(g)
7. Which of the processes A–D will lead to a positive change in the entropy of the system? If all of these processes lead
to a positive change in the entropy of the system, select E.
a.
Sodium chloride crystals form as saltwater evaporates.
b.
Helium gas escapes from the hole in a balloon.
c.
Stalactites form in a cave.
d.
Water freezes in a freezer.
e.
All of these lead to a positive change in entropy of the system, as they are all spontaneous.
8. Which of the following processes will lead to a decrease in the entropy of the system?
a.
Salt crystals dissolve in water.
b.
Air escapes from a hole in a balloon.
c.
Iron and oxygen react to form rust.
d.
Ice melts in your hand.
e.
None of these lead to a negative change in the entropy of the system, as they are all
spontaneous.
CALCULATING ΔS FOR REACTIONS (Math)
9. Determine ΔS for H
2
(g) + I
2
(g) D 2HI(g) given the following information.
Substance
S° (J/mol · K)
H
2
(g)
130.58
I
2
(g)
116.73
HI(g)
206.3
a.
–41.10 J/mol · K
d.
+165.29 J/mol · K
b.
–165.29 J/mol · K
e.
+41.10 J/mol · K
c.
+398.75 J/mol · K
10. Determine ΔS for N
2
O
4
(g) D 2NO
2
(g) given the following information.
Substance
S° (J/mol · K)
N
2
O
4
(g)
304.3
NO
2
(g)
240.45
a.
+176.7 J/mol · K
d.
–50.7 J/mol · K
b.
–63.8 J/mol · K
e.
–176.7 J/mol · K
c.
+63.8 J/mol · K
3
11. What is the entropy change to make 1 mole of SO
3
for the reaction SO
2
(g) + 1/2 O
2
(g) → SO
3
(g)
Substance
S° (J/mol · K)
SO
2
(g)
248.2
O
2
(g)
205.0
SO
3
(g)
256.8
a.
–196.4 J/K
d.
+93.9 J/K
b.
+196.4 J/K
e.
+401.4 J/K
c.
–93.9 J/K
12. NO gas is converted to NO
2
gas according to the following reaction, NO(g) + 1/2 O
2
(g) → NO
2
(g)
What is the standard entropy change when 0.5 mol of NO gas reacts with 0.5 mol of O
2
gas?
Substance
S° (J/mol · K)
NO(g)
210.7
O
2
(g)
205.0
NO
2
(g)
240.0
a.
–36.6 J/K
d.
+83.4 J/K
b.
–175.7 J/K
e.
+36.6 J/K
c.
–83.4 J/K
13. If 3.500 g of Ni (58.69 g/mol)are reacted with excess oxygen to form nickel oxide (NiO) under standard state
conditions, what is the entropy change for the reaction?
2Ni(s) + O
2
D 2NiO(s)
Substance
S° (J/mol · K)
Ni
182.1
O
2
205.0
NiO
37.99
a.
–49.3 J/K
d.
+49.3 J/K
b.
–24.7 J/K
e.
–10.4 J/K
c.
–14.7 J/K
14. What is the entropy change if 4.500 g of CaCO
3
(s) is placed in a container and allowed to decompose to CaO(s) and
CO
2
(g) according to the following reaction?
CaCO
3
(s) D CaO(s) + CO
2
(g)
Substance
S° (J/mol · K)
CaCO
3
(s)
92.88
CaO(s)
39.75
CO
2
(g)
213.6
a.
+7.2 J/K
d.
+160.5 J/K
b.
–160.5 J/K
e.
+3.57 J/K
c.
+35.7 J/K
15. What is the standard entropy change when 10.0 g of methane reacts with 10.0 g of oxygen?
CH
4
(g) + 2O
2
(g) → CO
2
(g) + 2H
2
O()
Substance
S° (J/mol · K)
CH
4
(g)
186.2
O
2
(g)
205.0
H
2
O(l)
70.0
CO
2
(g)
213.6
a.
–121 J/K
d.
–154.4 J/K
b.
–37.9 J/K
e.
–16.8 J/K
c.
–242.6 J/K
/ 7
End of Document
185

You May Also Like

FAQs

What are the key concepts covered in the thermodynamics practice problems?
The thermodynamics practice problems cover essential concepts such as entropy (ΔS), free energy (ΔG), and enthalpy (ΔH). Students will learn how to calculate these values for various chemical reactions and understand their significance in predicting reaction spontaneity. The problems also emphasize the relationship between entropy and the direction of chemical processes, providing a comprehensive overview of thermodynamic principles.
How do the practice problems help students understand spontaneity in reactions?
The practice problems are designed to help students evaluate the spontaneity of chemical reactions by analyzing changes in free energy and entropy. By working through various scenarios, students learn to apply the Gibbs free energy equation, ΔG = ΔH - TΔS, to determine whether a reaction will occur spontaneously under specific conditions. This hands-on approach reinforces theoretical knowledge and enhances problem-solving skills.
What types of calculations are included in the practice problems?
The practice problems include calculations for standard molar entropy, changes in entropy for reactions, and free energy changes. Students will encounter both qualitative and quantitative questions that require them to apply thermodynamic equations and principles. This variety ensures a well-rounded understanding of how to approach thermodynamic calculations in different contexts.
Who is the intended audience for these thermodynamics practice problems?
The intended audience includes high school students preparing for AP Chemistry exams and undergraduate students studying chemistry or related fields. The problems are tailored to reinforce classroom learning and provide additional practice for mastering thermodynamic concepts. This resource is particularly useful for students who need to strengthen their understanding of thermodynamics before exams.

Related