Identify each enthalpy change by name and classify each change as exothermic or endothermic.

1. 1 mol nacl (s) à 1 mol nacl(l)
2. c4h10 o(l) à c4h10o (g)
3. h2o(g) à h2o (l)
4. 1 mol nacl(s) + 3.88 kj/molà 1 mol nacl(aq)

a molar heat of solution; endothermic
b molar heat of vaporization; endothermic
c molar heat of fusion; endothermic
d molar heat of condensation; exothermic

1. C)

2. B)

3. D)

4. A)

Explanation:

Enthalpy change is the heat of the reaction measured at constant pressure.

i.e.

Chemical reactions are accompanied either by the absorption of heat (endothermic) or by the release of heat (exothermic)

1) 1 mol NaCl (s) ↔ 1 mol NaCl(l)

Ans: C) Molar heat of fusion; endothermic

Molar heat or enthalpy of fusion is the amount of energy absorbed when a solid melts into a liquid. It is an endothermic process since heat is absorbed.

2. C4H10 O(l) ↔ C4H10O (g)

Ans: B) Molar heat of vaporization; endothermic

Molar heat or enthalpy of vaporization is the amount of energy absorbed when a liquid evaporates into a gas. It is an endothermic process since heat is absorbed.

3. H2O(g) ↔ H2O (l)

Ans: D Molar heat of condensation; exothermic

Molar heat or enthalpy of condensation is the amount of energy released when a gas condenses into a liquid. It is an exothermic process since heat is released.

4. 1 mol NaCl(s) + 3.88 kJ/mol ↔ 1 mol NaCl(aq)

Ans: A) Molar heat of solution; endothermic

Heat of solution is the amount of heat absorbed when 1 mole of a substance is dissolved in water.