Question

Amongst the following, identify the criterion for a process to be at equilibrium.
A. $\;\Delta G < 0$
B. $\;\Delta G > 0$
C. $\Delta S$ total​=0
D. $\Delta S$<0

Answer 1

Gibbs free energy or the free energy is the representation of the sum total energy of the system which is required by the system for performing work. At the constant values for temperature and pressure the relationship between free energy and entropy change given by $\Delta G$and $\Delta S$respectively is as follows:
$\Delta G = \Delta H - T\Delta S................(1)$, at equilibrium entropy change of the system is zero.

Complete step by step answer:
Now using the relationship between free energy and entropy change given by $\Delta G$and $\Delta S$, given by $\Delta G = \Delta H - T\Delta S$ we can find out either forward or backward reaction will take place or equilibrium will be attained.
First we will discuss if $\Delta G$ is less than 1
Substituting in equation 1, then we find that the reaction proceeds in forward reaction.
If $\Delta G$ is greater than 1
Substituting in equation 1, then we find that the reaction proceeds in a backward reaction.
If $\Delta G$ is equal to 0
Substituting in equation 1, then we find that the reaction equilibrium is attained.
Now if $\Delta G$, we see that $\Delta S$ will also be zero.

So, the correct answer is Option C.

Note: In general terms equilibrium is defined as the stage at which the rate of reactions are equal, that is the rate at which forward reaction occurs is equal to the rate at which backward reaction occurs. At this point equilibrium reactant molecules combine to form products and these products formed can disassociate back to form reactants. Equilibrium is said to be in a dynamic state as it shifts from reactant to products.