AP CHEMISTRY
Week 6 Problem Set
Solutions
, AP Chemistry Week 6
Problem Set Solution
Multiple Choice Questions
Question 1: Which of the following best helps to explain why the value of Δ H ° for the
dissolving of 𝐶𝑎𝐹2 in water is positive?
A) 𝐶𝑎𝐹2 (𝑠) is insoluble in water
B) 𝐶𝑎𝐹2 (𝑠) dissolves in water to form 𝐶𝑎𝐹2 (𝑎𝑞) particles
C) 𝐶𝑎2+ ions have very strong ion-ion interactions with 𝐹 − ions in the crystal lattice
D) 𝐶𝑎2+ ions have very strong ion-dipole interactions with water molecules in the
solution
Answer: C is correct. ∆H is positive which means that the reactant must be more stable
than the products in the dissolution equation. Therefore, the bonds in the lattice must
be stronger.
CaF2(s) Ca2+ (aq) + 2F - (aq)
A) explains the solubility of the CaF2 but doesn’t explain why ∆H⁰ is positive. Recall
that ∆H⁰ depends on the potential energy of the products and reactants.
B) does not explain why ∆H is positive
D) would be the case if dissolution was exothermic and the ∆H⁰ was negative.
Question 2: A 10.g cube of copper at a temperature T 1 is placed in an insulated cup
containing 10.g of water at a temperature T 2. If T 1 >T 2, 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·°C) and the specific heat of water is 4.18 J / (g∙ ℃).)
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.
02
Week 6 Problem Set
Solutions
, AP Chemistry Week 6
Problem Set Solution
Multiple Choice Questions
Question 1: Which of the following best helps to explain why the value of Δ H ° for the
dissolving of 𝐶𝑎𝐹2 in water is positive?
A) 𝐶𝑎𝐹2 (𝑠) is insoluble in water
B) 𝐶𝑎𝐹2 (𝑠) dissolves in water to form 𝐶𝑎𝐹2 (𝑎𝑞) particles
C) 𝐶𝑎2+ ions have very strong ion-ion interactions with 𝐹 − ions in the crystal lattice
D) 𝐶𝑎2+ ions have very strong ion-dipole interactions with water molecules in the
solution
Answer: C is correct. ∆H is positive which means that the reactant must be more stable
than the products in the dissolution equation. Therefore, the bonds in the lattice must
be stronger.
CaF2(s) Ca2+ (aq) + 2F - (aq)
A) explains the solubility of the CaF2 but doesn’t explain why ∆H⁰ is positive. Recall
that ∆H⁰ depends on the potential energy of the products and reactants.
B) does not explain why ∆H is positive
D) would be the case if dissolution was exothermic and the ∆H⁰ was negative.
Question 2: A 10.g cube of copper at a temperature T 1 is placed in an insulated cup
containing 10.g of water at a temperature T 2. If T 1 >T 2, 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·°C) and the specific heat of water is 4.18 J / (g∙ ℃).)
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.
02
