Chapter 17, Problem 71A

(a)

Interpretation Introduction

Interpretation:

The name of the enthalpy changes and whether the reaction is exothermic or endothermic is to be found.

Concept Introduction :

Endothermic reactions are those reactions in which heat is absorbed. The enthalpy change for the endothermic reaction is positive.

Exothermic reactions are those reactions in which heat is released. The enthalpy change for the endothermic reaction is negative.

Answer to Problem 71A

The enthalpy change will be enthalpy of vaporization and the reaction is endothermic.

Explanation of Solution

  ${\text{1mol C}}_{\text{3}}{\text{H}}_{\text{8}}\text{(l)}\to {\text{1mol C}}_{\text{3}}{\text{H}}_{\text{8}}\text{(g)}$

The enthalpy of vaporization is the heat energy required to transform the liquid state to a gaseous state at constant pressure.

Vaporization is the process where the liquid phase is changed to the gaseous phase. The energy must be absorbed by liquid to weaken the intermolecular forces and convert into a more random state called a gaseous state.

(b)

Interpretation Introduction

Interpretation:

The name of the enthalpy changes and whether the reaction is exothermic or endothermic is to be found.

Concept Introduction :

Endothermic reactions are those reactions in which heat is absorbed. The enthalpy change for an endothermic reaction is positive.

Exothermic reactions are those reactions in which heat is released. The enthalpy change for an endothermic reaction is negative.

Answer to Problem 71A

The enthalpy change will be the enthalpy of solidification and the reaction is exothermic.

Explanation of Solution

  $\text{1mol Hg(l)}\to \text{1mol Hg(s)}$

The enthalpy of solidification is the heat energy released to transform a liquid state to a solid state at constant pressure.

Solidification is the process where the liquid phase is changed to the solid phase. The energy must be released by liquid to strengthen the intermolecular forces and convert into a less random solid state.

(c)

Interpretation Introduction

Interpretation:

The name of the enthalpy changes and whether the reaction is exothermic or endothermic is to be found.

Concept Introduction : Endothermic reactions are those reactions in which heat is absorbed. The enthalpy change for the endothermic reaction is positive.

Exothermic reactions are those reactions in which heat is released. The enthalpy change for the endothermic reaction is negative.

Answer to Problem 71A

The enthalpy change will be the enthalpy of condensation and the reaction is exothermic.

Explanation of Solution

  ${\text{1mol NH}}_3\text{(g)}\to {\text{1mol NH}}_3\text{(l)}$

The enthalpy of condensation is the heat energy released to transform a gaseous state to a liquid state at constant pressure.

Condensation is the process where the gaseous phase is changed to the liquid phase. The energy must be released by gas to strengthen the intermolecular forces to change into a liquid.

(d)

Interpretation Introduction

Interpretation:

The name of the enthalpy changes and whether the reaction is exothermic or endothermic is to be found.

Concept Introduction:

Endothermic reactions are those reactions in which heat is absorbed. The enthalpy change for the endothermic reaction is positive.

Exothermic reactions are those reactions in which heat is released. The enthalpy change for the endothermic reaction is negative.

Answer to Problem 71A

The enthalpy change will be the enthalpy of the solution and the reaction is endothermic.

Explanation of Solution

  $\text{1mol NaCl(s)+3}\text{.88 kJ}\to \text{1mol NaCl(aq)}$

Enthalpy of the solution is the heat energy absorbed or released to dissolve a substance at constant pressure resulting in infinite dilution.

As the heat is shown on the reactant side, it means the heat has been absorbed and thus, the reaction is endothermic.