Chapter 6, Problem 6.31P

(a)

Interpretation Introduction

Interpretation:

Whether the value of $w_{\text{sys}}$ in the phase change represented in the scene is positive $(+)$, negative $(-)$, or zero is to be determined.

Concept introduction:

Work $\left(w\right)$ is the energy needed to move an object in the opposite direction of the force applied. The work done by the system is negative and the work done on the system is positive. The formula to calculate the work done against external pressure is as follows:

$w=-P\Delta V$        (1)

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.

The formula to calculate $\Delta V$ of the system is as follows:

$\Delta V=V_{\text{Final}}-V_{\text{Initial}}$        (2)

(b)

Interpretation Introduction

Interpretation:

Whether the value of $H_{\text{sys}}$ in the phase change represented in the scene is positive $(+)$, negative $(-)$, or zero 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:

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

Or,

$\Delta H=q_p$        (3)

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.

$q_p$ is the heat absorbed or released at constant pressure.

(c)

Interpretation Introduction

Interpretation:

Whether the value of $\Delta E_{\text{system}}$ in the phase change represented in the circle is positive $(+)$, negative $(-)$, or zero 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.

Heat $\left(q\right)$ is the energy transferred as a consequence of the difference of the temperature between the system and surrounding.

Work $\left(w\right)$ is the energy needed to move an object in the opposite direction of the force applied.

The expression to calculate $\left(\Delta E\right)$ is as follows:

$\Delta E=q+w$        (4)

Here,

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

$q$ is the heat released or absorbed.

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