Entropy Calculator
Calculate entropy change (ΔS) for chemical reactions, gas expansion, or temperature changes. Uses standard thermodynamic formulas.
Select the type of entropy calculation
Standard molar entropies of products in J/mol·K
Standard molar entropies of reactants in J/mol·K
Number of moles of gas (for isothermal calculation)
Initial volume in liters
Final volume in liters
Starting temperature in Kelvin
Ending temperature in Kelvin
Heat capacity in J/mol·K
What is entropy?
Entropy (S) is a measure of disorder or randomness in a system. In chemistry, standard molar entropy (S°) is at 298 K and 1 atm, measured in J/mol·K. More ordered states (solids) have lower entropy; more disordered states (gases) have higher entropy. The second law states total entropy always increases in spontaneous processes.
How do you calculate entropy change?
For reactions: ΔS°_rxn = ΣS°_products - ΣS°_reactants. For gas expansion at constant T: ΔS = nRln(V2/V1). For temperature change at constant pressure: ΔS = nCp ln(T2/T1). At constant volume: ΔS = nC_v ln(T2/T1).
What is the relationship between entropy and Gibbs free energy?
ΔG = ΔH - TΔS connects Gibbs free energy to entropy. At constant T and P: if ΔS > 0, the reaction becomes more spontaneous at higher T. For a spontaneous process: ΔS_total = ΔS_system + ΔS_surroundings > 0. Entropy drives spontaneity.
Why do gases have higher entropy than liquids?
Gas molecules move freely with many more possible arrangements than liquids or solids. More microstates (possible configurations) means higher entropy. Standard molar entropy: S°(gas) ~150-200 J/mol·K, S°(liquid) ~50-80 J/mol·K, S°(solid) ~20-50 J/mol·K.Phase changes increase entropy dramatically.