Question

The criteria for a spontaneous process is:
A. $\Delta G>0$
B. $\Delta G<0$
C. $\Delta G=0$
D. $\Delta {{S}_{total}}<0$

Answer 1

Hint: Spontaneous process is basically a reaction that favours the formation of products at the various conditions under which reaction is occurring. It is characterised by a decrease in the system’s free energy, so they do not need to be driven by an outside source of energy.

Complete step by step solution:
-As we know that for a spontaneous process the change in entropy is positive. And it is positive when in any system there is disorder or randomness.
-$\Delta G$ is known as Gibbs free energy, it is the net free energy available to do useful work. And we also called it free energy of the reaction.
-It is found that if any reaction is to be spontaneous then at a given temperature and pressure, the Gibbs energy of the system should decrease, that is it must be negative.
-So, we can say that for a process to be spontaneous should be less than zero at a given pressure and temperature, that is $\Delta G<0$

Hence, we can conclude that the correct option is (B), that is the criteria for a spontaneous process is $\Delta G<0$.

Note: - We should not get confused between Gibbs free energy and Helmholtz free energy. The difference between both of these is that Gibbs free energy change is basically used when we consider processes that occur under constant temperature and pressure.
- Whereas, Helmholtz free energy change is used when we consider processes that occur under constant temperature and volume.