heat engines thermodynamics

Question

What is the entropy change of a gas in J/K (to 2 decimal points) when one mole of a perfect gas reversibly expands from 0.36 m³ to 2.42 m³?

Answer 1

For free expansion of a perfect (or ideal) gas, one would set down the change in entropy

equal to the number of moles times the Universal Gas Constant times the natural logarithm of the

ratio of the resultant volume to the initial volume.

Then write ΔS = nR_uln (V₂/V₁) or

(1 mole) × (8.31451070 Joules per mole per Kelvin) × ln (2.42 m³/0.36 m³).

This last simplifies to 15.8426249 Joules Per Kelvin or 15.84 J/K.