# Formula: Entropy Change Due To Volume Change Entropy    Amount of substance    Gas constant    Volume

## Entropy change

Unit
The entropy change $$\Delta S = S_2 - S_1$$ of an ideal gas from the initial value $$S_1$$ to the final value $$S_2$$.

## Amount of substance

Unit
The amount of substance $$n$$ indicates the number of particles (atoms, molecules, or ions) in a substance. It is defined as the ratio of the particle count $$N$$ to the Avogadro's constant $$N_{\text A} = 6.022\,140\,76 \cdot 10^{23} \, \frac{1}{\mathrm{mol}}$$: $$n ~=~ \frac{N}{N_{\text A}}$$

In one mole of a substance, there are approximately $$6 \cdot 10^{23}$$ particles.

## Gas constant

Unit
Molar gas constant (also called universal gas constant) is a physical constant from thermodynamics and has the following exact value: $$R ~=~ 8.314 \, 462 \, 618 \, 153 \, 24 \, \frac{\mathrm J}{\mathrm{mol} \, \mathrm{K}}$$

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