Entropy, like energy is a fundamental abstract thermodynamic concept. It is not difficult, as we have already seen, to state the essential mathematical properties of the entropy function S. The first point to recognize is that entropy is not a thing. There are no entropy meters. Entropy is not a directly measurable quantity, but rather entropy changes are calculated from measurable quantities such as temperature, pressure, volume, heat capacity, current and magnetic field strength.

*Entropy change can be calculated as the difference between the entropy of the product and entropy of reactants. So, the formula is,***Entropy was described by the great thermodynamist J.Willard Gibbs as a measure of the "mixed-up-ness" of a system; that is, the more disordered or randomized a system is, the higher is its entropy.**$\Delta S_{Reaction}$ = $\Delta S_{Products}$ - $\Delta S_{Reactants}$

**Step 1:**Analyze the given measures

**Step 2:**Put these quantities in the given equation

$\Delta S_{Reaction}$ = $\Delta S_{Products}$ - $\Delta S_{Reactants}$

Solved problems based on entropy are given in this section.

### Solved Examples

**Question 1:**Calculate the entropy of the product, if the total entropy and the entropy of the reactants are 105J/K/mol and 25J/K/mol respectively.

**Solution:**

Given parameters are,

$\Delta S_{Reaction}$ = 105J/K/mol

$\Delta S_{Reactants}$ = 25J/K/mol

Formula to find out the entropy change is,

$\Delta S_{Reaction}$ = $\Delta S_{Products}$ - $\Delta S_{Reactants}$

105 = $\Delta S_{Products}$ - 25

$\Delta S_{Products}$ = 105 + 25 = 130J/K/mol

**Question 2:**Calculate the entropy of the reaction, if the entropy of the product and the entropy of the reactants are 98J/K/mol and 50J/K/mol respectively.

**Solution:**

Given parameters are,

$\Delta S_{Products}$ = 98J/K/mol

$\Delta S_{Reactants}$ = 50J/K/mol

Formula to find out the entropy change is,

$\Delta S_{Reaction}$ = $\Delta S_{Products}$ - $\Delta S_{Reactants}$

$\Delta S_{Reaction}$ = 98 - 50 = 48J/K/mol