Chapter 6, Problem 6.56P

Interpretation Introduction

Interpretation:

Whether the value of $\Delta H$ when 1 mol of water vapor condenses to liquid water is positive or negative is to be determined. Also, its comparison with $\Delta H$ for the vaporization of $2\text{ mol}$ of liquid water to water vapor is to be done.

Concept introduction:

The internal energy of a process is the summation of the kinetic energy and potential energy associated with the process. In chemical reactions, the change in internal energy $\left(\Delta E\right)$ is the difference in the energy of the product and reactant but at constant pressure, the $P\Delta V$ work gets eliminated and the change in enthalpy $\left(\Delta H\right)$ is measured.

In chemical reactions, the change in enthalpy $\left(\Delta H\right)$ is the difference in the energy of the product and reactant. The general expression to calculate $\Delta H$ is,

$\Delta H=H_{\text{Product}}-H_{\text{Reactant}}$ (1)

Here,

$\Delta H$ is the change in enthalpy of the system.

$H_{\text{Product}}$ is the enthalpy of the products.

$H_{\text{Reactant}}$ is the enthalpy of the reactants.

Endothermic reactions are the reactions in which energy in the form of the heat or light is absorbed by the reactant for the formation of product. $H_{\text{Product}}$ is greater than $H_{\text{Reactant}}$ in the endothermic reactions.

Exothermic reactions are the reactions in which energy in the form of the heat or light is released with the product. $H_{\text{Reactant}}$ is greater than $H_{\text{Product}}$ in the exothermic reactions.