,Verified CHEM 103 Module 5 Exam-General
Chemistry I-Portage - (26/27) Actual (PDF)
1. A chemical reaction that releases heat to its surroundings is classified as:
A) Endothermic
B) Exothermic
C) Isothermic
D) Adiabatic
Correct Answer: B) Exothermic
Rationale: Exothermic reactions release energy (usually as heat) to the surroundings, causing the
surroundings to warm. The sign of ΔH is negative for exothermic reactions. Endothermic (A) absorbs
heat, isothermic (C) means constant temperature, and adiabatic (D) means no heat exchange.
2. Which of the following best defines enthalpy (H)?
A) The total kinetic energy of all molecules in a system
B) The heat content of a system at constant pressure
C) The measure of disorder in a system
D) The energy required to break all bonds in one mole of substance
Correct Answer: B) The heat content of a system at constant pressure
Rationale: Enthalpy is defined as the heat content of a system at constant pressure, represented by H
in thermochemical equations. Option A describes kinetic energy, C describes entropy, and D describes
bond energy.
3. A reaction releases 850 kJ of energy. What is the sign of ΔH for this reaction?
A) Positive; the reaction is endothermic
B) Negative; the reaction is exothermic
C) Positive; the reaction is exothermic
D) Negative; the reaction is endothermic
Correct Answer: B) Negative; the reaction is exothermic
,Rationale: When energy is released by a reaction, ΔH is negative and the reaction is classified as
exothermic. The negative sign indicates that energy leaves the system and enters the surroundings.
Option A describes endothermic (ΔH > 0), C has the wrong sign convention, and D is incorrect.
4. Calculate the heat required to raise the temperature of 50.0 g of water from 25.0°C to 75.0°C.
(Specific heat of water = 4.184 J/g·°C)
A) 5,230 J
B) 10,460 J
C) 15,690 J
D) 20,920 J
Correct Answer: B) 10,460 J
Rationale: q = m × c × ΔT = 50.0 g × 4.184 J/g·°C × (75.0 - 25.0)°C = 50.0 × 4.184 × 50.0 = 10,460 J.
Option A is for a 25°C change, C is for a 75°C change, and D is for a 100°C change.
5. In a calorimetry experiment, 50.0 grams of water at 25°C absorbs 2,500 joules of heat. What is the
final temperature of the water? (Specific heat of water = 4.18 J/g·°C)
A) 26.0°C
B) 27.0°C
C) 36.99°C
D) 46.99°C
Correct Answer: C) 36.99°C
Rationale: Using q = mcΔT, ΔT = q/(mc) = 2,500 J / (50.0 g × 4.18 J/g·°C) = 2, = 11.96°C. Final
temperature = 25 + 11.96 = 36.96°C ≈ 36.99°C. Option A is incorrect, B is incorrect, and D is incorrect.
6. Calculate the energy required to melt 120 g of ice at 0°C. (Heat of fusion for water = 0.334 kJ/g)
A) 40.08 kJ
B) 120 kJ
C) 0.334 kJ
D) 359 kJ
Correct Answer: A) 40.08 kJ
, Rationale: q = mass × ΔH_fus = 120 g × 0.334 kJ/g = 40.08 kJ. Option B is the mass in grams, C is the
heat of fusion per gram, and D is incorrect.
7. Calculate the energy released when 25.0 g of water at 100°C condenses to liquid water at 100°C.
(Heat of vaporization for water = 2.26 kJ/g)
A) 25.0 kJ
B) 56.5 kJ
C) 2.26 kJ
D) 113 kJ
Correct Answer: B) 56.5 kJ
Rationale: q = mass × ΔH_vap = 25.0 g × 2.26 kJ/g = 56.5 kJ (released, so negative). Option A is the
mass, C is the heat of vaporization per gram, and D is double.
8. In a thermochemical equation, the ΔH value is negative. This indicates that the reaction is:
A) Endothermic
B) Exothermic
C) Neither exothermic nor endothermic
D) Not enough information
Correct Answer: B) Exothermic
Rationale: A negative ΔH indicates that the reaction releases heat to the surroundings, which is the
definition of an exothermic reaction. A positive ΔH (A) indicates an endothermic reaction. Options C
and D are incorrect.
9. Given the thermochemical equation: 2 S + 3 O₂ → 2 SO₃ ΔH = -792 kJ. If 42.8 g of S reacts with excess
O₂, what is the heat given off? (Atomic mass S = 32.07 g/mol)
A) -792 kJ
B) -526.7 kJ
C) -1053.4 kJ
D) -264.3 kJ
Correct Answer: B) -526.7 kJ
Chemistry I-Portage - (26/27) Actual (PDF)
1. A chemical reaction that releases heat to its surroundings is classified as:
A) Endothermic
B) Exothermic
C) Isothermic
D) Adiabatic
Correct Answer: B) Exothermic
Rationale: Exothermic reactions release energy (usually as heat) to the surroundings, causing the
surroundings to warm. The sign of ΔH is negative for exothermic reactions. Endothermic (A) absorbs
heat, isothermic (C) means constant temperature, and adiabatic (D) means no heat exchange.
2. Which of the following best defines enthalpy (H)?
A) The total kinetic energy of all molecules in a system
B) The heat content of a system at constant pressure
C) The measure of disorder in a system
D) The energy required to break all bonds in one mole of substance
Correct Answer: B) The heat content of a system at constant pressure
Rationale: Enthalpy is defined as the heat content of a system at constant pressure, represented by H
in thermochemical equations. Option A describes kinetic energy, C describes entropy, and D describes
bond energy.
3. A reaction releases 850 kJ of energy. What is the sign of ΔH for this reaction?
A) Positive; the reaction is endothermic
B) Negative; the reaction is exothermic
C) Positive; the reaction is exothermic
D) Negative; the reaction is endothermic
Correct Answer: B) Negative; the reaction is exothermic
,Rationale: When energy is released by a reaction, ΔH is negative and the reaction is classified as
exothermic. The negative sign indicates that energy leaves the system and enters the surroundings.
Option A describes endothermic (ΔH > 0), C has the wrong sign convention, and D is incorrect.
4. Calculate the heat required to raise the temperature of 50.0 g of water from 25.0°C to 75.0°C.
(Specific heat of water = 4.184 J/g·°C)
A) 5,230 J
B) 10,460 J
C) 15,690 J
D) 20,920 J
Correct Answer: B) 10,460 J
Rationale: q = m × c × ΔT = 50.0 g × 4.184 J/g·°C × (75.0 - 25.0)°C = 50.0 × 4.184 × 50.0 = 10,460 J.
Option A is for a 25°C change, C is for a 75°C change, and D is for a 100°C change.
5. In a calorimetry experiment, 50.0 grams of water at 25°C absorbs 2,500 joules of heat. What is the
final temperature of the water? (Specific heat of water = 4.18 J/g·°C)
A) 26.0°C
B) 27.0°C
C) 36.99°C
D) 46.99°C
Correct Answer: C) 36.99°C
Rationale: Using q = mcΔT, ΔT = q/(mc) = 2,500 J / (50.0 g × 4.18 J/g·°C) = 2, = 11.96°C. Final
temperature = 25 + 11.96 = 36.96°C ≈ 36.99°C. Option A is incorrect, B is incorrect, and D is incorrect.
6. Calculate the energy required to melt 120 g of ice at 0°C. (Heat of fusion for water = 0.334 kJ/g)
A) 40.08 kJ
B) 120 kJ
C) 0.334 kJ
D) 359 kJ
Correct Answer: A) 40.08 kJ
, Rationale: q = mass × ΔH_fus = 120 g × 0.334 kJ/g = 40.08 kJ. Option B is the mass in grams, C is the
heat of fusion per gram, and D is incorrect.
7. Calculate the energy released when 25.0 g of water at 100°C condenses to liquid water at 100°C.
(Heat of vaporization for water = 2.26 kJ/g)
A) 25.0 kJ
B) 56.5 kJ
C) 2.26 kJ
D) 113 kJ
Correct Answer: B) 56.5 kJ
Rationale: q = mass × ΔH_vap = 25.0 g × 2.26 kJ/g = 56.5 kJ (released, so negative). Option A is the
mass, C is the heat of vaporization per gram, and D is double.
8. In a thermochemical equation, the ΔH value is negative. This indicates that the reaction is:
A) Endothermic
B) Exothermic
C) Neither exothermic nor endothermic
D) Not enough information
Correct Answer: B) Exothermic
Rationale: A negative ΔH indicates that the reaction releases heat to the surroundings, which is the
definition of an exothermic reaction. A positive ΔH (A) indicates an endothermic reaction. Options C
and D are incorrect.
9. Given the thermochemical equation: 2 S + 3 O₂ → 2 SO₃ ΔH = -792 kJ. If 42.8 g of S reacts with excess
O₂, what is the heat given off? (Atomic mass S = 32.07 g/mol)
A) -792 kJ
B) -526.7 kJ
C) -1053.4 kJ
D) -264.3 kJ
Correct Answer: B) -526.7 kJ
