Question

What is the physical significance of Gibbs function?
(A) Decreases in Gibbs function is the measure of the useful work done by the system.
(B) Increase in Gibbs function is the measure of the useful work done by the system.
(C) Decreases in Gibbs function is the measure of the useful heat loss by the system.
(D) Nine.

Answer 1

Gibbs free energy tells us about feasibility of reaction. It means that it tells whether the reaction takes place or not.
Change in Gibbs free energy gives the reaction and extent reaction.

Complete step by step answer:
Gibbs free energy is energy available in the system to do work.
Some conditions of change in Gibbs energy are given as follows.
(i) $\Delta G < 0$ the process is spontaneous
(ii) $\Delta G > 0$ the process is non spontaneous
(iii) $\Delta G = 0$ the process is in equilibrium
The reaction is spontaneous when Gibbs energy is zero.
Decrease in Gibb’s function at constant temperature and pressure in a process gives maximum work.
This work is non-PV work (useful work)
PV work means pressure volume type of work.
The work is maximum when it takes place in a reversible manner.
Therefore, maximum work is obtained when it has to be done at constant temperature and pressure and in reversible manner.
And Gibb’s function decreases at constant temperature and pressure in PV type works in a reversible manner.
Therefore, from the above explanation the correct option is (A) Decreases in Gibbs function is the measure of the useful work done by the system.
i.e., Decrease in Gibb’s function is the measure of useful work done by the system.
Change in Gibbs energy
$\Delta G = - T\Delta S$ total
Where, $T =$ absolute temperature
$\Delta s$ change in entropy

Note:
The value of $\Delta G$ tells us whether a physical or chemical change occurs spontaneously.
$\Delta G$ depends on $\Delta H$ and $\Delta S$ where
$\Delta H$ is change in enthalpy
$\Delta S$ is change in entropy
And the negativity of $\Delta G$ depends on the value of $\Delta S$ and $\Delta H$ at high temperature or low temperature.