Question

A process will be spontaneous to all temperature if:
A. $\Delta H > 0 and \Delta S < 0$
B. $\Delta H < 0 and \Delta S > 0$
C. $\Delta H > 0 and \Delta S > 0$
D. $\Delta H < 0 and \Delta S < 0$

Answer 1

. A spontaneous process is generally a thermodynamic process. It is generally a time-evolution system in which it releases free energy and moves to a lower i.e. more thermodynamically stable energy state.

Complete step by step answer:
In this process the sign convention for free energy change follows the general observation for thermodynamic calculations in which a release of free energy from the system corresponds to a negative change in the free energy of the system and a positive change in the free energy of the surroundings. Also spontaneous process is the process which can take place by itself. Example of spontaneous process is flow of water down a hill.
To find out if the reaction is spontaneous or not we use Gibbs free energy which is equal to the enthalpy of the system minus the product of the temperature and entropy. The equation of Gibbs free energy can be given by
$G = H - TS$
But we generally consider the change in Gibbs free energy which can be shown by the formula
$\Delta G=\Delta H-T\Delta S$, for a reaction to be spontaneous at all temperature, $\Delta G < 0$or we can say that change in gibbs free energy should be negative and it is possible only when $\Delta H < 0$ and $\Delta S > 0$ only this conditions make $\Delta G<0$.
So, the correct answer is “Option B”.

Note: $\Delta G < 0$ tells us about the reactions spontaneity that is spontaneous in nature when$\Delta G < 0$. If $\Delta G > 0$ then reaction is non spontaneous in nature while if change in Gibbs free energy is 0 then the reaction is at equilibrium. $\Delta G$ also tells us about the direction and extent of chemical change.