Chapter 8, Problem 8.21NP

(a)

Interpretation Introduction

Interpretation: The vapor pressure of benzene (l) at 340.0 K needs to be determined, if the vapor pressure of benzene is 0.1269 bar at 298.15 K and the enthalpy of vaporization is 30.72 kJ/mol. Also, it is assumed that the enthalpy of vaporization does not change with temperature.

The value of ${\text{C}}_{\text{p,m}}$ of the vapor and liquid phase at that temperature are 82.4 and 136.0 J/K respectively.

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.

Similarly, the gases can be compressed at high pressure to liquefy. 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 ${\text{ΔH}}_{\text{vap}}$ .

(b)

Interpretation Introduction

Interpretation: The vapor pressure of benzene needs to be determined at 340.0 K, if the vapor pressure of benzene is 0.1269 bar at 298.15 K and the enthalpy of vaporization is 30.72 kJ/mol. Also, it is assumed that the enthalpy of vaporization at T is calculated from below equation:

  $\Delta {\text{H}}_{\text{vap}}\text{(T)}\text{}\text{ = }\Delta {\text{H}}_{\text{vap}}{\text{(T}}_{\text{0}}\text{)}\text{}+\Delta {\text{C}}_{\text{p}}{\text{(T-T}}_{\text{0}}\text{)}\text{}$

The value of ${\text{C}}_{\text{p,m}}$ of the vapor and liquid phase at that temperature is 82.4 and 136.0 J/K respectively.

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.

Similarly, the gases can be compressed at high pressure to liquefy. 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 ${\text{ΔH}}_{\text{vap}}$ .