Thermodynamics Practice Questions I with Answers

1. A chemical reaction that absorbs heat from the surroundings is said to be __________ and has a __________ ∆H at constant pressure.
   • A) endothermic, positive
   • B) endothermic, negative
   • C) exothermic, negative
   • D) exothermic, positive
   • E) exothermic, neutral

2. The value of ∆H for the reaction below is -126 kJ. How much heat (in kJ) is released when 2.00 mol of NaOH is formed in the reaction?

2Na₂O₂ (s) + 2H₂O (l) ¬ 4NaOH (s) + O₂ (g)

• A) 252
• B) -126
• C) 7.8
• D) 63
• E) 3.9

3. The specific heat of liquid bromine is 0.226 J/g-K. How much heat (J) is required to raise the temperature of 10.0 mL of bromine from 25.00ºC to 27.30ºC? The density of liquid bromine: 3.12 g/mL.
   • A) 16.2
   • B) 10.4
   • C) 32.4
   • D) 5.20
   • E) 300

4. Which is true if ∆H is -95J?
   • A) Both the system and the surroundings are gaining 95 J
   • B) Both the system and the surroundings are losing 95 J
   • C) The system is gaining 95J and the surroundings are losing 95 J
   • D) The system is losing 95J and the surroundings are gaining 95 J
   • E) The system is gaining 95J and the surroundings are gaining 95 J

5. Which statement about enthalpy is true?
   • A) Heat is given off to the surroundings in endothermic reactions.
   • B) Some substances have a negative specific heat capacity.
   • C) Specific heat capacity is the same for all liquids.
   • D) The sign of ∆H is always negative in exothermic reactions.

6. What happens to the value of ∆H for a thermochemical reaction if the reaction is reversed?
   • A) ∆H has the same numerical value, and the sign changes.
   • B) ∆H has the same numerical value, and the sign remains the same.
   • C) ∆H is the reciprocal of the original value, and the sign changes.
   • D) ∆H is the reciprocal of the original value, and the sign remains the same.

7. Which of the following processes is exothermic?
   • A) Ether evaporating
   • B) Ice melting
   • C) Steam condensing
   • D) Water decomposing

8. Calculate the work for the expansion of CO₂ from 1.0 to 4.7 liters against a pressure of 1.0 atm at constant temperature.
   • A) 3.7 L atm
   • B) 4.7 L atm
   • C) 0 L atm
   • D) -3.7 L atm
   • E) -4.7 L atm

9. Using the data below, what is the order of changes that occur when ethanol is heated from -25.0ºC to 85.0ºC?

Boiling point of ethanol: 78.5ºC                 Melting point of ethanol: -117.3ºC

• A) Phase change, temperature change
• B) Phase change, temperature change, phase change
• C) Temperature change, phase change
• D) Temperature change, phase change, temperature change

10. The value of ∆H for the reaction below is -336 kJ. Calculate the heat (kJ) released to the surroundings when 23.0 g of HCl is formed.

CH₄ (g) + 3Cl₂ (g) ¬ CHCl₃ (l) + 3HCl (g)

• A) 211
• B) 177
• C) 70.7
• D) -336
• E) 2.57 x 103

11. Which of the following properties is (are) intensive properties?
    • mass
    • temperature
    • . volume
    • concentration
    • energy

• A) I, III, and V
• B) II only
• C) II and IV
• D) III and IV
• E) I and V

12. How much heat is required to raise the temperature of a 5.75-g sample of iron (specific heat = 0.450 J/g°C) from 25.0°C to 79.8°C?
    • A) 2.54 J
    • B) 315 J
    • C) 700 J
    • D) 848 J
    • E) 142 J

12. Two metals of equal mass with different heat capacities are subjected to the same amount of heat. Which undergoes the smallest change in temperature?
    • A) The metal with the higher heat capacity.
    • B) The metal with the lower heat capacity.
    • C) Both undergo the same change in temperature.
    • D) You need to know the initial temperatures of the metals.
    • E) You need to know which metals you have.

14. A 32.5 g piece of aluminum (which has a molar heat capacity of 24.03 J/°C·mol) is heated to 82.4°C and dropped into a calorimeter containing water (specific heat capacity of water is 4.18 J/g°C) initially at 22.3°C. The final temperature of the water is 24.2°C. Ignoring significant figures, calculate the mass of water in the calorimeter.
    • A) 212 g
    • B) 5.72 kg
    • C) 6.42 g
    • D) 1.68 kg
    • E) none of these

15. A 45.9 g sample of a metal is heated to 95.2°C and then placed in a calorimeter containing 120.0 g of water (c = 4.18 J/g°C) at 21.6°C. The final temperature of the water is 24.5°C. Which metal was used?
    • A) Aluminum (c = 0.89 J/g°C)
    • B) Iron (c = 0.45 J/g°C)
    • C) Copper (c = 0.20 J/g°C)
    • D) Lead (c = 0.14 J/g°C)
    • E) none of these

16. You take 295.5 g of a solid at 30.0°C and let it melt in 425 g of water. The water temperature decreases from 85.1°C to 30.0°C. Calculate the heat of fusion of this solid.
    • A) 160 J/g
    • B) 166 J/g
    • C) 331 J/g
    • D) 721 J/g
    • E) cannot solve without the heat capacity of the solid

17. The enthalpy of fusion of ice is 6.020 kJ/mol. The heat capacity of liquid water is 75.4 J/mol·°C. What is the smallest number of ice cubes at 0°C, each containing one mole of water, necessary to cool 500 g of liquid water initially at 20°C to 0°C?
    • A) 1
    • B) 7
    • C) 14
    • D) 15
    • E) 126

18. 0 mL of pure water at 282 K is mixed with 50.0 mL of pure water at 306 K. What is the final temperature of the mixture?
    • A) 294 K
    • B) 297 K
    • C) 342 K
    • D) 588 K
    • E) 24 K

19. Consider the reaction

H₂(g) + O₂(g) àH₂O(l)     ∆H° = –286 kJ

Which of the following is true?

• A) The reaction is exothermic.
• B) The reaction is endothermic.
• C) The enthalpy of the products is less than that of the reactants.
• D) Heat is absorbed by the system.
• E) Both A and C are true.

20. What is the specific heat capacity of a metal if it requires 178.1 J to change the temperature of 15.0 g of the metal from 25.00°C to 32.00°C?
    • A) 0.590 J/g°C
    • B) 11.9 J/g°C
    • C) 25.4 J/g°C
    • D) 1.70 J/g°C
    • E) 283 J/g°C

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