Unit 7: Thermochemistry

51. What is the process called when a solid changes directly into a gas without passing through the liquid phase?

a) Condensation
b) Sublimation
c) Deposition
d) Vaporization
Answer: b) Sublimation

52. Which of the following reactions will have a higher enthalpy change when carried out at constant volume compared to constant pressure?

a) Reactions involving solids
b) Reactions involving liquids
c) Reactions involving gases
d) Reactions involving aqueous solutions
Answer: c) Reactions involving gases

53. In which process does entropy decrease?

a) Evaporation of water
b) Dissolving sugar in water
c) Crystallization of a salt from a solution
d) Mixing two gases
Answer: c) Crystallization of a salt from a solution

54. The standard state of a substance refers to its form at:

a) 0°C and 1 atm pressure
b) 25°C and 1 atm pressure
c) 0°C and 0.1 atm pressure
d) 25°C and 0.1 atm pressure
Answer: b) 25°C and 1 atm pressure

55. Which of the following statements is true for an endothermic reaction?

a) ΔH is negative
b) The temperature of the surroundings decreases
c) The products have lower energy than the reactants
d) Heat is released to the surroundings
Answer: b) The temperature of the surroundings decreases

56. Which of the following thermodynamic quantities is a measure of energy dispersal?

a) Enthalpy
b) Entropy
c) Internal energy
d) Free energy
Answer: b) Entropy

57. The heat required to raise the temperature of a substance by 1 degree Celsius is called:

a) Specific heat
b) Molar heat capacity
c) Heat of fusion
d) Heat of vaporization
Answer: b) Molar heat capacity

58. The enthalpy change for the breaking of a chemical bond is:

a) Always positive
b) Always negative
c) Zero
d) Depends on the bond
Answer: a) Always positive

59. Which of the following factors influences the spontaneity of a reaction?

a) Temperature
b) Enthalpy change
c) Entropy change
d) All of the above
Answer: d) All of the above

60. Which of the following processes is spontaneous?

a) Melting of ice at 0°C
b) Freezing of water at 25°C
c) Rusting of iron
d) Decomposition of water into hydrogen and oxygen
Answer: c) Rusting of iron