Chapter 6, Problem 6.17P

Interpretation Introduction

Interpretation:

Among $\Delta H$ and $\Delta E$ the one that is more convenient to measure is to be determined.

Concept introduction:

The internal energy of a process is the summation of the kinetic energy and potential energy associated with the process. In the case of a reaction, 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. The relationship $\Delta E$ and $\Delta H$ is as follows:

$\Delta H=\Delta E+P\Delta V$

Here,

$\Delta E$ is the change in internal energy of the system.

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

$P$ is the external pressure.

$\Delta V$ is the change in the volume.

The formula to calculate $\Delta E$ of the system is:

$\Delta E=q+w$

Here,

$\Delta E$ is the change in internal energy of the system.

$q$ is the heat released or absorbed.

$w$ is the work done by the system or on the system.

The formula to calculate the work done against an external pressure is:

$w=-P\Delta V$

Here,

$w$ is the work done by the system or on the system.

$P$ is the external pressure.

$\Delta V$ is the change in the volume.