CHEM 121 MODULE 5:
THERMOCHEMISTRY, GASES, AND
INTERMOLECULAR FORCES
QUESTIONS AND ANSWERS 2026/2027
UPDATE || 100% GUARANTEED PASS
1. A system releases 150 J of heat while performing 50 J of work on the surroundings. What is
the change in internal energy (ΔE) of the system?
A. +200 J
B. -100 J
C. -200 J
D. +100 J
Answer: C
Conceptual Explanation: According to the first law of thermodynamics, ΔE = q + w. Since
heat is released, q = -150 J. Since work is done by the system, w = -50 J. ΔE = -150 + (-50) = -
200 J.
2. Under what conditions do real gases deviate most significantly from ideal behavior?
A. Low temperature and high pressure
B. High temperature and low pressure
,C. High temperature and high pressure
D. Low temperature and low pressure
Answer: A
Conceptual Explanation: Real gases deviate from ideal behavior at low temperatures
(where IMFs become significant) and high pressures (where the volume of molecules is no
longer negligible).
3. Calculate the final temperature when 50.0 g of water at 80.0°C is mixed with 50.0 g of
water at 20.0°C (Specific heat of water = 4.184 J/g°C).
A. 60.0°C
B. 40.0°C
C. 50.0°C
D. 30.0°C
Answer: C
Conceptual Explanation: Since the masses and specific heats are identical, the final
temperature is the simple average: (80+20)/2 = 50°C.
4. A gas occupies 2.0 L at 300 K. What is the volume if the temperature is increased to 600 K
at constant pressure?
A. 1.0 L
B. 4.0 L
, C. 2.0 L
D. 8.0 L
Answer: B
Conceptual Explanation: According to Charles’s Law (V1/T1 = V2/T2), volume is directly
proportional to absolute temperature. Doubling T doubles V.
5. Which of the following substances would exhibit the highest boiling point due to hydrogen
bonding?
A. HF
B. H2S
C. NH3
D. CH4
Answer: A
Conceptual Explanation: HF has stronger hydrogen bonding than NH3 because Fluorine is
more electronegative than Nitrogen. CH4 and H2S do not exhibit hydrogen bonding.
6. What is the standard enthalpy of formation (ΔHf°) for any element in its most stable form
at 25°C?
A. 1.0 kJ/mol
B. 0 kJ/mol
C. -1.0 kJ/mol
THERMOCHEMISTRY, GASES, AND
INTERMOLECULAR FORCES
QUESTIONS AND ANSWERS 2026/2027
UPDATE || 100% GUARANTEED PASS
1. A system releases 150 J of heat while performing 50 J of work on the surroundings. What is
the change in internal energy (ΔE) of the system?
A. +200 J
B. -100 J
C. -200 J
D. +100 J
Answer: C
Conceptual Explanation: According to the first law of thermodynamics, ΔE = q + w. Since
heat is released, q = -150 J. Since work is done by the system, w = -50 J. ΔE = -150 + (-50) = -
200 J.
2. Under what conditions do real gases deviate most significantly from ideal behavior?
A. Low temperature and high pressure
B. High temperature and low pressure
,C. High temperature and high pressure
D. Low temperature and low pressure
Answer: A
Conceptual Explanation: Real gases deviate from ideal behavior at low temperatures
(where IMFs become significant) and high pressures (where the volume of molecules is no
longer negligible).
3. Calculate the final temperature when 50.0 g of water at 80.0°C is mixed with 50.0 g of
water at 20.0°C (Specific heat of water = 4.184 J/g°C).
A. 60.0°C
B. 40.0°C
C. 50.0°C
D. 30.0°C
Answer: C
Conceptual Explanation: Since the masses and specific heats are identical, the final
temperature is the simple average: (80+20)/2 = 50°C.
4. A gas occupies 2.0 L at 300 K. What is the volume if the temperature is increased to 600 K
at constant pressure?
A. 1.0 L
B. 4.0 L
, C. 2.0 L
D. 8.0 L
Answer: B
Conceptual Explanation: According to Charles’s Law (V1/T1 = V2/T2), volume is directly
proportional to absolute temperature. Doubling T doubles V.
5. Which of the following substances would exhibit the highest boiling point due to hydrogen
bonding?
A. HF
B. H2S
C. NH3
D. CH4
Answer: A
Conceptual Explanation: HF has stronger hydrogen bonding than NH3 because Fluorine is
more electronegative than Nitrogen. CH4 and H2S do not exhibit hydrogen bonding.
6. What is the standard enthalpy of formation (ΔHf°) for any element in its most stable form
at 25°C?
A. 1.0 kJ/mol
B. 0 kJ/mol
C. -1.0 kJ/mol
