20. The following reaction has a ΔG° value of 48.71 kJ/mol at 25°C.
HB(aq) + H₂O(l) ⇌ H₃O⁺(aq) + B^-(aq)
Calculate the Ka for the acid HB.
(A) 0.981
(B) -19.7
(C) 2.89 x 10^-9
(D) 4.87 x 10^-5
(E) -234

1. Boron consists of two naturally occurring isotopes, ¹⁰B and ¹¹B. Bromine also has two naturally occurring isotopes, ⁷⁹Br and ⁸¹Br. How many molecular-ion peaks would be expected in the mass spectrum of BBr₃? (A) 2 (B) 4 (C) 6 (D) 8 (E) 12

2. A balloon has a volume of 3.02 L at 27°C. The balloon is heated to 127°C at constant pressure. What is the new volume of the balloon? (A) 2.82 L (B) 3.27 L (C) 4.03 L (D) 4.88 L (E) 14.2 L

3. For the following hypothetical reactions,  I. A₂(g) + B₂(g) ⇌ 2AB(g) K_I = 10²  II. 2A₂(g) + C₂(g) ⇌ 2A₂C(g) K_II = 10⁻⁴ III. A₂C(g) + B₂(g) ⇌ 2AB(g) + 1/2 C₂(g) What is the equilibrium constant, K, for reaction III? (A) 10⁻² (B) 10² (C) 10⁴ (D) 10⁶ (E) 10⁸

4. Nitrogen gas reacts with hydrogen gas to form ammonia: N₂(g) + 3H₂(g) ⇌ 2NH₃(g) At 200°C in a rigid container, 1.2 atm of N₂ and 2.3 atm of H₂ are mixed. At equilibrium, the total pressure is 2.1 atm. What is the equilibrium partial pressure of H₂? (A) 0.92 atm (B) 0.20 atm (C) 1.2 atm (D) 1.8 atm (E) 0.35 atm

5. According to the Brønsted-Lowry definition, an acid is (A) a substance that increases the hydrogen ion concentration in solution. (B) a substance that increases the hydroxide ion concentration in solution. (C) a substance that can donate a proton to another species. (D) a substance that can accept a proton from another species. (E) an electron pair acceptor.

6. Which of the following 0.01 M aqueous solutions has the highest pH value? (A) HOAc (B) NaHCO₃ (C) H₂CO₃ (D) NaOAc (E) Na₂CO₃

7. Consider a solution of 2.0 M HCN (K_a = 6.2 × 10⁻¹⁰) and 1.0 M NaCN. Which statement is true? (A) The solution is not a buffer because [HCN] is not equal to [CN⁻]. (B) The buffer is more resistant to pH changes from added strong acid than from added strong base. (C) [OH⁻] > [H⁺] (D) The pH is below 7.00 because the concentration of the acid is greater than that of the base. (E) All of these statements are false.

8. At constant pressure, the reaction 2 NO₂(g) → N₂O₄(g) is exothermic. The reaction, as written, is (A) spontaneous at high temperatures but not at low temperatures. (B) spontaneous at low temperatures but not at high temperatures. (C) always spontaneous. (D) never spontaneous. (E) not possible to determine the spontaneity from the information given.

9. A calorimeter contains 95 g of water at 25.0°C. A 5.0 g sample of ice at -5.0°C is added, and eventually all the ice melts. Calculate the final temperature of the water. Assume no heat is lost to the calorimeter or the surroundings. The specific heat capacities for water and ice are 4.200 and 2.060 J g⁻¹°C⁻¹, respectively. The heat of fusion of ice is 334 J/g. (A) 19.6°C (B) 17.5°C (C) 20.7°C (D) 21.2°C

10. When 1.00 mol of a pure liquid is vaporized at a constant pressure of 1.00 atm and at its boiling point of 320.0 K, 28.80 kJ of heat is absorbed, and the volume change is +24.90 L. What is ΔE for this process? (A) -31.32 kJ (B) +31.32 kJ (C) -26.28 kJ (D) +26.28 kJ

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