Question

For a spontaneous process, which of the following is true?
A: $\Delta {S_{sys}}$ is positive
B: $\Delta {S_{surr}}$ is positive
C: $\Delta {S_{total}}$ is positive
D: $\Delta {S_{total}}$ is negative

Answer 1

A spontaneous process is a process which proceeds in a given direction without being driven by an outside energy source. While, a non-spontaneous process (also called an endergonic process) is a chemical process in which energy is being absorbed and standard change in the free energy is positive.

Complete step by step answer:
Spontaneous process releases the free energy as they proceed. This free energy involved in the process is most commonly known as Gibbs free energy and is denoted by G in the name of an American scientist i.e. Josiah Gibbs who contributed to thermodynamics in many ways.
The determining factors in case of a spontaneous process are enthalpy ($\Delta H$) as well as entropy ($\Delta S$) changes which occur for the system. Mathematically, change in the Gibbs free energy ($\Delta G$) can be computed with the following expression:
$\Delta G = \Delta H - T\Delta S$
A spontaneous process releases free energy which means that ΔG must be negative (< 0). This means that $\Delta H$must be less than $T\Delta S$. As a result, $\Delta {S_{total}}$must be positive.

Hence, the correct answer is Option C.

Note:
Always remember that the temperature in Gibbs free energy expression is the Kelvin temperature, thus, it can only possess a positive value. If $\Delta H$is negative and $\Delta S$is positive, $\Delta G$ is negative, indicating that the process is spontaneous at all the temperatures. In other cases if $\Delta H$is positive and $\Delta S$is negative, $\Delta G$is positive, indicating that the process is nonspontaneous.