Entropy Change Calculator (ΔS)
Find the standard entropy change of a reaction by subtracting the total reactant entropy from the total product entropy.
Negative ΔS: entropy (disorder) decreases.
- 1
Sum of product entropies Σ(n·S°)
213.7 + 69.9 = 283.6 J/mol·K - 2
Sum of reactant entropies Σ(m·S°)
186.3 + 205 = 391.3 J/mol·K - 3
ΔS°rxn = products − reactants
283.6 − 391.3 = -107.70Positive ΔS means products are more disordered than reactants.
How does this calculator work?
Standard reaction entropy equals the total standard entropy of the products minus that of the reactants, each weighted by its stoichiometric coefficient. Enter your n·S° values in J/mol·K for products and reactants; the calculator sums each side and subtracts to give ΔS°rxn, where a positive result signals increasing disorder.
Formula
How this is calculated
The reaction entropy change measures how the disorder of a chemical system shifts from reactants to products. Enter the standard molar entropy values for each product and each reactant, with every number already multiplied by its stoichiometric coefficient (n · S°). Values are separated by commas or new lines and are expressed in joules per mole per kelvin (J/mol·K).
The calculator sums the product list and the reactant list independently, then applies ΔS°rxn = Σ(n · S°products) − Σ(m · S°reactants). A positive ΔS° means the products are more disordered than the reactants (common when moles of gas increase or solids dissolve), while a negative ΔS° indicates a more ordered final state.
Standard molar entropies are absolute values referenced to 0 K (Third Law of Thermodynamics) and are tabulated at 298.15 K and 1 bar, so the result represents the standard entropy change at those conditions. Because every element and compound has a positive S°, remember to weight each species by its coefficient before entering it. Leaving one list empty treats its total as zero.
Frequently asked questions
Reaction entropy weights each species by how many moles appear in the balanced equation. Multiply the stoichiometric coefficient by the species standard molar entropy (n · S°) before entering it so the totals reflect the actual amounts.
A positive value means the products have greater entropy (disorder) than the reactants, which often happens when the number of gas molecules increases or a solid becomes a liquid or gas.
Standard molar entropies and the resulting ΔS°rxn are in J/mol·K. To combine with enthalpy (often in kJ/mol) for ΔG, convert entropy to kJ/mol·K by dividing by 1000.
Also known as
TG we-Calculate Editorial Team. (2026). Entropy Change Calculator (ΔS) [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/entropy-change-calculator
TG we-Calculate Editorial Team. "Entropy Change Calculator (ΔS)." TG we-Calculate. 2026. https://we-calculate.com/calculator/entropy-change-calculator.
TG we-Calculate Editorial Team, "Entropy Change Calculator (ΔS)," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/entropy-change-calculator
@misc{wecalculate_entropy_change_calculator, title = {Entropy Change Calculator (ΔS)}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/entropy-change-calculator}}, year = {2026}, note = {TG we-Calculate} }
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