Entropy Calculator
Calculate entropy changes for chemical reactions, Gibbs free energy, and isothermal gas processes
Calculate Entropy Changes
Quick Select Common Substances (Standard Entropy Values)
Click to add to products total (modify as needed)
Reaction Entropy Change
Analysis:
Calculation: 0 - 0 = 0.00 J/(mol·K)
Quick Examples
Water Formation
2H₂ + O₂ → 2H₂O
ΔS = -326.4 J/(mol·K)
Entropy decreases (gas → liquid)
Ice Melting
H₂O(s) → H₂O(l)
ΔS = +22.0 J/(mol·K)
Entropy increases (order → disorder)
Gas Expansion
Volume doubles at constant T
ΔS = nR ln(2) = +5.76n J/K
Always positive for expansion
Standard Entropy Values
*Values in J/(mol·K) at 298.15 K
Understanding Entropy and Thermodynamics
What is Entropy?
Entropy (S) is a measure of disorder or randomness in a system. It quantifies the number of microscopic configurations that correspond to a thermodynamic system's macroscopic state. The second law of thermodynamics states that the entropy of the universe tends toward a maximum.
Key Entropy Concepts
- •Gases have higher entropy than liquids and solids
- •Higher temperature increases entropy
- •More complex molecules have higher entropy
- •Mixing increases entropy
Entropy Calculations
Chemical Reactions
ΔS°reaction = ΣS°products - ΣS°reactants
Use standard entropy values at 298.15 K
Gibbs Free Energy
ΔG = ΔH - TΔS
Determines reaction spontaneity
Isothermal Gas Processes
Volume: ΔS = nR ln(V₂/V₁)
Pressure: ΔS = -nR ln(P₂/P₁)
For ideal gases at constant temperature
Entropy and Spontaneity
ΔS > 0
Entropy increases. Favors spontaneity. System becomes more disordered.
ΔS < 0
Entropy decreases. Opposes spontaneity. System becomes more ordered.
ΔG Relationship
Both ΔH and ΔS contribute to spontaneity through the Gibbs free energy equation.