Chapter 12, Problem 12.12P

Interpretation Introduction

Interpretation:

The two processes on the macroscopic and molecular levels that occur when benzene is at its melting point are to be determined.

Concept introduction:

The phase is defined as the physical state of a substance. The properties of a phase are determined by the interaction of the potential energy $\left(E_p\right)$ and kinetic energy $\left(E_{\text{k}}\right)$ of particles. There are three major phases as follows:

1) Solid

2) Liquid

3) Gas

In gases, the value of kinetic energy $\left(E_{\text{k}}\right)$ is greater than potential energy $\left(E_p\right)$ so the particles can move freely without any force of attraction towards each other while in the case of solids, the value of $E_p$ is greater than $E_{\text{k}}$ so the solid particle cannot move freely and remain vibrating at one place. In the case of liquids, the potential energy $\left(E_p\right)$ is greater as compared to gases but still, the particles can move but less than the gases.

When a solid phase is converted into a liquid phase and when a liquid freeze it changes to a solid phase. The phase changes can be expressed as follows:

$\text{Solid}\underset{\text{Freezing}}{\overset{\text{Melting}}{\rightleftarrows }}\text{Liquid}$