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Identify the correct statement for change of Gibbs energy for a system ($\Delta G_{system}$) at constant temperature and pressure :-
A
If $\Delta G_{system} \gt 0$, the process is spontaneous
B
If $\Delta G_{system} = 0$, the system has attained equilibrium
C
If $\Delta G_{system} = 0$, the system is still moving in a particular direction
D
If $\Delta G_{system} \lt 0$, the process is not spontaneous
Detailed Solution
At constant temperature and pressure, the Gibbs energy change $\Delta G = \Delta H - T\Delta S$ is the criterion of spontaneity.
If $\Delta G_{system} \lt 0$, the process is spontaneous.
If $\Delta G_{system} \gt 0$, the process is non-spontaneous (the reverse process is spontaneous).
If $\Delta G_{system} = 0$, the process is in equilibrium; there is no net change in either direction.
So the statements saying that $\Delta G \gt 0$ is spontaneous, that $\Delta G \lt 0$ is not spontaneous, and that at $\Delta G = 0$ the system is still moving in a particular direction are all wrong.
The correct statement is: if $\Delta G_{system} = 0$, the system has attained equilibrium.
If $\Delta G_{system} \lt 0$, the process is spontaneous.
If $\Delta G_{system} \gt 0$, the process is non-spontaneous (the reverse process is spontaneous).
If $\Delta G_{system} = 0$, the process is in equilibrium; there is no net change in either direction.
So the statements saying that $\Delta G \gt 0$ is spontaneous, that $\Delta G \lt 0$ is not spontaneous, and that at $\Delta G = 0$ the system is still moving in a particular direction are all wrong.
The correct statement is: if $\Delta G_{system} = 0$, the system has attained equilibrium.