During the phase transition, at constant temperature, of a solid from one form to another, the change in molar volume, $$\Delta V_m = 1.0\,\text{cm}^3\text{mol}^{-1}$$ is independent of pressure. The change in molar Gibbs free energy, in units of $$J mol^{-1}$$, ​when the pressure in increased from 1 bar to 3 bars is

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Correct option is C

The molar Gibbs free energy is a thermodynamic property of a substance that describes its potential to do non-mechanical work (such as chemical reactions) at constant temperature and pressure. It is denoted by the symbol G and is usually measured in joules per mole (J/mol) or sometimes in kilojoules per mole (kJ/mol).

Mathematically, the molar Gibbs free energy is defined as:

G=H-TS

dG= dH- TdS-SdT

dG=Vdp -SdT

where

G is the molar Gibbs free energy, H is the molar enthalpy (total heat content) of the system, T is the absolute temperature (in K) and S is the molar entropy.

During phase change, the temperature of the system remains constant, dT=0

dG=Vdp

$$\left( \frac{\partial G}{\partial n} \right) = V_m \, dp$$​

$$\mu = V_m \, dp$$​

According to question, during the phase transition, at constant temperature, of a solid from one form to another, the change in molar volume, ΔV_m=1cm³mol^-1 is independent of pressure.

When the pressure is increased from 1bar to 3 bar,

​1cm³mol^-1(3bar-1bar)