Chapter 8, Problem 8.29NP

Interpretation Introduction

Interpretation: This is to be proved that a substance having coexisting solid-liquid curve and a negative slope contracts upon melting.

Concept Introduction: All substances can mainly exist in three phases; solid, liquid and gases. These three phases can convert into each other by the application of temperature and pressure such as by heating of solid, it converts to liquid and then gaseous state of matter.

The enthalpy change during the fusion of solid to liquid is called as enthalpy of fusion that is denoted as ${\text{ΔH}}_{\text{fus}}$ . Similarly the enthalpy of vaporization involves in the vaporization of liquid to gas is called as enthalpy of vaporization that is denoted as ${\text{ΔH}}_{\text{vap}}$ .

Clausius - Clapeyron equation purposed the relationship between the pressure and temperature for conditions of equilibrium between two phases; vapor and solid for sublimation or solid and liquid for fusion.

  $\text{ln}\frac{{\text{P}}_{\text{f}}}{{\text{P}}_{\text{i}}}\text{=}\frac{{\text{ΔH}}_{\text{vap}}}{\text{R}}\left(\frac{\text{1}}{{\text{T}}_{\text{f}}}\text{-}\frac{\text{1}}{{\text{T}}_{\text{i}}}\right)$

Here, P is pressure, T is temperature, R is Universal gas constant and ${\text{ΔH}}_{\text{vap}}$ is change in enthalpy of vaporization.