Question

Define critical temperature and critical pressure. In terms of the kinetic molecular theory, why is it impossible for a substance to exist as a liquid above its critical temperature?

Short answer

Critical temperature(Tc)– The temperature at which the vapors are not able to liquefy the pressure would be whatever.

$\mathrm{Tc}=\frac{8\mathrm{a}}{27\mathrm{Rb}}$

Critical Pressure (Pc)– The pressure at which it is applied to make the liquefaction of vapor at the critical temperature.

$\mathrm{Pc}=\frac{\mathrm{a}}{27{\mathrm{b}}^2}$

The critical point defines the critical temperature and critical pressure.

Step-by-step solution

Step 1:Critical temperature and critical pressure

Critical temperature(Tc)– The temperature at which the vapors cannot liquefy the pressure would be whatever.

$\mathrm{Tc}=\frac{8\mathrm{a}}{27\mathrm{Rb}}$

Critical Pressure (Pc)– The pressure at which it is applied to make the liquefaction of vapor at the critical temperature.

$\mathrm{Pc}=\frac{\mathrm{a}}{27{\mathrm{b}}^2}$

The critical point defines the critical temperature and critical pressure.

Explanation

According to the kinetic molecular theory, as the temperature of molecules rises gradually, that leads to a rise in the average kinetic energy of molecules.

Above the critical temperature, the average kinetic energyof molecules is high, and these molecules move randomly in any direction with negligible intermolecular forcesin the liquid state.

Hence, it is impossible to exist in the liquid phase above the critical temperature.