Calculate the total change in entropy (ΔS) for a reaction by taking the difference between the entropy of products and reactants.
Reaction Properties
J/K
J/K
Calculation Results
Enter standard entropy values to calculate ΔS
About this calculator
Overview
Entropy (S) is a thermodynamic quantity that measures the degree of randomness or disorder in a system. The change in entropy (ΔS) indicates the direction of sponteneity for a process.
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Pro Tips
ΔS = ΣS(products) - ΣS(reactants) is the standard formula for chemical reactions.
Standard molar entropy (S°) values are typically measured at 298.15 K and 1 atm.
A positive ΔS suggests an increase in disorder, which favors spontaneity according to Gibbs Free Energy.
Phase changes (solid → liquid → gas) lead to massive jumps in entropy due to increased molecular mobility.
Dissolving a solid in a solvent usually increases entropy as the crystalline structure breaks down.
Reactions that produce more gas molecules than they consume always have a positive ΔS.
Units are J/(mol·K) – much smaller than Enthalpy units (kJ/mol), so convert carefully when calculating ΔG!
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Fun Facts
"The Second Law of Thermodynamics states that the total entropy of an isolated system can never decrease over time."
"Entropy is often called the 'Arrow of Time' because it defines the forward direction of universal processes."
"Melting ice increases entropy because water molecules move more freely than in rigid ice crystal structures."
"The universe tends toward maximum entropy, a state theoretical physicists call the 'Heat Death of the Universe'."
"Ludwig Boltzmann's tombstone in Vienna is engraved with his entropy formula: S = k ln W."
"Zero entropy occurs only at absolute zero (0 K), a state required by the Third Law of Thermodynamics."
"Information entropy, a concept from computer science, uses the same mathematical framework as thermodynamic entropy."
"Life is a 'local' decrease in entropy; living organisms maintain order by exporting disorder (heat) to their surroundings."
Formula: ΔS = ΣSₚ - ΣSᵣ
Entropy Changes in Common Processes
Visualizing how entropy shifts across different physical and biological transformations.
