132 ❯ STEP 4. Review the Knowledge You Need to Score High
- When ammonium chloride dissolves in water,
the temperature drops. Which of the following
conclusions may be related to this?
(A) Ammonium chloride is more soluble in hot
water.
(B) Ammonium chloride produces an ideal solu-
tion in water.
(C) The heat of solution for ammonium chloride
is exothermic.
(D) Ammonium chloride has a low lattice energy. - Which of the following reactions is expected to
have the greatest increase in entropy?
(A) H 2 O(g) → H 2 O(l)
(B) 2 KClO 3 (s) → 2 KCl(s) + 3 O 2 (g)
(C) Ca(s) + H 2 (g) → CaH 2 (s)
(D) N 2 (g) + 3 H 2 (g) → 2 NH 3 (g) - Magnesium metal reacts readily with liquid bro-
mine under standard conditions. Which of the fol-
lowing conclusions may be drawn from this fact?
(A) Keq < 1 and ΔG° > 0
(B) Keq > 1 and ΔG° = 0
(C) Keq < 1 and ΔG° < 0
(D) Keq > 1 and ΔG° < 0 - Which of the following combinations is true
when sodium chloride melts?
(A) ΔH > 0 and ΔS > 0
(B) ΔH = 0 and ΔS > 0
(C) ΔH > 0 and ΔS < 0
(D) ΔH < 0 and ΔS < 0 - Which of the following reactions has a negative
entropy change?
(A) 2 C 2 H 6 (g) + 7 O 2 (g) → 4 CO 2 (g) + 6 H 2 O(g)
(B) 2 NH 3 (g) → N 2 (g) + 3 H 2 (g)
(C) CaCl 2 (s) → Ca(s) + Cl 2 (g)
(D) 2 H 2 (g) + O 2 (g) → 2 H 2 O(l) - A certain reaction is nonspontaneous under
standard conditions but becomes spontaneous at
higher temperatures. What conclusions may be
drawn under standard conditions?
(A) ΔH < 0, ΔS > 0, and ΔG > 0
(B) ΔH > 0, ΔS < 0, and ΔG > 0
(C) ΔH > 0, ΔS > 0, and ΔG > 0
(D) ΔH < 0, ΔS < 0, and ΔG > 0
13. 2 H 2 (g) + O 2 (g) → 2 H 2 O(l)
From the table below, determine the enthalpy
change for the above reaction.
BONDAVERAGE BOND ENERGY
(kJ/mol)
H–H 436
O=O 499
H–O 464
(A) 0 kJ
(B) 485 kJ
(C) –485 kJ
(D) 464 kJ- Which of the following reactions is accompanied
by the greatest increase in entropy?
(A) 2 H 2 (g) + O 2 (g) → 2 H 2 O(g)
(B) 2 Mn 2 O 7 (l) → 4 MnO 2 (s) + 3 O 2 (g)
(C) 2 C(s) + O 2 (g) → 2 CO(g)
(D) 2 Mg(s) + O 2 (g) → 2 MgO(s) - Hydrogen gas burns in oxygen gas according to
the following reaction:
2 H 2 (g) + O 2 (g) → 2 H 2 O(l) ΔH = - 572 kJ
What is the energy change when 2.00 moles of
water decompose to the elements at constant
pressure?
(A) –286 kJ
(B) –572 kJ
(C) +572 kJ
(D) +286 kJ - A solution is prepared by dissolving solid ammo-
nium nitrate, NH 4 NO 3 , in water. The initial tem-
perature of the water was 25°C, but after the solid
had dissolved, the temperature fell to 20°C. What
conclusions may be made about ΔH and ΔS?
(A) ΔH < 0 and ΔS > 0
(B) ΔH > 0 and ΔS > 0
(C) ΔH > 0 and ΔS < 0
(D) ΔH < 0 and ΔS < 0