Question

For which of the following processes $\Delta S$ is > 0 ?
A) $\text{MgC}{{\text{O}}_{3}}(~\text{s})\to \text{MgO}(\text{s})+\text{C}{{\text{O}}_{2}}(~\text{g})$
B) $2 \mathrm{I}(\mathrm{g}) \rightarrow \mathrm{I}_{2}(\mathrm{~g})$
C) $\mathrm{Na}^{+}(\mathrm{g})+\mathrm{Cl}(\mathrm{g}) \rightarrow \mathrm{NaCl}(\mathrm{s})$
D) ${{\text{H}}_{2}}\text{O}(\text{l})\to {{\text{H}}_{2}}\text{O}(\text{s})$

Answer 1

Entropy is a quantifiable physical characteristic that is most frequently linked with a condition of disorder, unpredictability, or uncertainty. The word and idea are utilised in a wide range of areas, from classical thermodynamics, where it was originally identified, through statistical physics' microscopic description of nature, to information theory's principles.

Complete answer:
A spontaneous process in thermodynamics is one that happens without any external input to the system. The time-evolution of a system in which it releases free energy and goes to a lower, more thermodynamically stable energy state is a more technical definition (closer to thermodynamic equilibrium). The sign convention for free energy change is the same as for thermodynamic measurements, with a release of free energy from the system resulting in a negative change in the system's free energy and a positive change in the free energy of the surroundings.
It is critical to carefully evaluate the definition of the system and surroundings when utilising the entropy change of a process to measure spontaneity. The second rule of thermodynamics asserts that if the entropy of an isolated system rises over time, the process will be spontaneous. The sentence must be adjusted for open or closed systems to say that the total entropy of the combined system and surroundings must rise.
When a system's particles have more freedom of motion, its entropy rises. When there are more moles of gaseous products than reactants, and when there are more product particles in solution than reactant particles, the entropy increases. As a result, the entropy of the provided reactions rises.
$\text{MgC}{{\text{O}}_{3}}(~\text{s})\to \text{MgO}(\text{s})+\text{C}{{\text{O}}_{2}}(~\text{g})$
Because the reactant side has no gaseous particles and the product side has one, As a result, entropy rises, and $\Delta S$ rises above zero.

Note:
The free energy is calculated differently depending on the nature of the operation. When examining processes that occur under constant pressure and temperature circumstances, for example, the Gibbs free energy change is employed, but the Helmholtz free energy change is utilised when analysing processes that occur under constant volume and temperature conditions. Temperature, pressure, and volume can affect the value and even the sign of both free energy changes.