Thermodynamics (MC)

Question 1

Which of the following equations represents a reaction for which the standard entropy change is positive (∆Sº > 0)?

a. 3O₂(g) ⇒ 2O₃(g)
b. 2H₂(g) + O₂(g) ⇒ 2H₂O(l)
c. CaCO₃(s) ⇒ CaO(s) + CO₂(g)
d. I₂(g) + 2K(s) ⇒ 2KI(s)

Answer 1

C

Question 2

A 10. g cube of copper at a temperature T₁ is placed in an insulated cup containing 10. g of water at a temperature T₂. If T₁ > T₂, which of the following is true of the system when it has attained thermal equilibrium? (The specific heat of copper is 0.385 J / (g ºC) and the specific heat of water is 4.18 J / (g ºC).)

a. The temperature of the copper changed more than the temperature of the water.
b. The temperature of the water changed more than the temperature of the copper.
c. The temperature of the water and the copper changed by the same amount.
d. The relative temperature changes of the copper and the water cannot be determined without knowing T₁ and T₂

Answer 2

A

Question 3

FeF₂(s) ⇒ Fe²⁺(aq) + 2F^-(aq) K₁ = 2 x 10^-6

F^-(aq) + H⁺(aq) ⇒ HF(aq) K₂ = 1 x 10³

FeF₂(s) + 2H⁺(aq) ⇒ Fe²⁺(aq) + 2HF(aq) K₃ = ?

On the basis of the information above, the dissolution of FeF₂(s) in acidic solution is

a. Thermodynamically favorable, because K₂ > 1
b. Thermodynamically favorable, because K₃ > 1
c. Not thermodynamically favorable, because K₁ < 1
d. Not thermodynamically favorable, because K₃ < 1

Answer 3

B

Question 4

This question refers to the following graph, which shows the heating curve for methane, CH₄.

How much energy is required to melt 64 g of methane at 90 K? (The molar mass of methane is 16 g / mol).

a. 0.24 kJ
b. 3.8 kJ
c. 33 kJ
d. 60. kJ

Answer 4

B

Question 5

XY₂ ⇒ X + Y₂

The equation above represents the decomposition of a compound XY₂. The diagram below shows two reaction profiles (path one and path two) for the decomposition of XY₂.

Which of the following best describes the flow of heat when 1.0 mol of XY₂ decomposes?

a. 50 kJ of heat is transferred to the surroundings.
b. 50 kJ of heat is transferred from the surroundings.
c. 100 kJ of heat is transferred to the surroundings.
d. 100 kJ of heat is transferred from the surroundings.

Answer 5

B

Question 6

XY₂ ⇒ X + Y₂

The equation above represents the decomposition of a compound XY₂. The diagram below shows two reaction profies (path one and path two) for the decomposition of XY₂.

The reaction is thermodynamically favorable under standard conditions at 298 K. Therefore, the value of ∆Sº for the reaction must be

a. equal to zero
b. equal to ∆Hº / 298 K
c. greater than ∆Hº / 298 K
d. less than ∆Hº / 298 K

Answer 6

C