Entropy Change Calculator
Reaction Entropy (ΔS°rxn)
ΔS°rxn = ΣS°products - ΣS°reactants
Entropy of Phase Change
ΔS = ΔH / T at the phase transition temperature
Entropy of Surroundings
ΔS_surr = -ΔH_sys / T
Formula
ΔS°rxn = ΣS°products - ΣS°reactants | ΔS = ΔH/T (phase change) | ΔS_surr = -ΔH_sys/T
Frequently Asked Questions
What is entropy?
Entropy (S) is a measure of the disorder or randomness of a system. The Second Law of Thermodynamics states that the total entropy of the universe always increases for spontaneous processes. Units: J/(mol·K).
How do I predict the sign of ΔS?
ΔS is positive (increase) when: gases are produced, number of moles increases, solids dissolve, temperature increases. ΔS is negative when: gases condense, precipitation occurs, fewer moles of gas form.
What is the relationship between entropy and spontaneity?
A process is spontaneous when ΔS_universe > 0, i.e., ΔS_system + ΔS_surroundings > 0. This is equivalent to ΔG < 0 (Gibbs free energy). A reaction can be spontaneous even if ΔS_system < 0 if ΔS_surroundings is large enough.
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