Entropy Change of an Ideal Gas Calculator

About this calculator

Entropy is the thermodynamic measure of a system's disorder, and for an ideal gas undergoing any process, the change in entropy can be split cleanly into a temperature-dependent term and a volume-dependent term: ΔS = nCv·ln(T2/T1) + nR·ln(V2/V1), where n is the moles of gas, Cv is the molar heat capacity at constant volume, and R is the universal gas constant. Heating a gas or letting it expand both increase its entropy, and this formula quantifies exactly how much.

This calculator takes the moles, heat capacity, and initial/final temperatures and volumes and computes the total entropy change. It's a standard calculation in physical chemistry and chemical engineering thermodynamics courses, used to analyze whether a process is reversible, to evaluate the efficiency of heat engines and refrigeration cycles, and to check compliance with the second law of thermodynamics, which requires total entropy to never decrease in an isolated system.