Enthalpy/Entropy Calculator
Thermodynamic context
Thermodynamic datasets often mix unit systems for ΔH and ΔS. The most common source of error is combining inconsistent units in Gibbs calculations.
\[\Delta G = \Delta H - T\cdot\Delta S\]
\[1\,\mathrm{cal}=4.184\,\mathrm{J},\quad 1\,\mathrm{kcal}=4184\,\mathrm{J}\]
This page converts values and performs automatic consistency checks in the Gibbs mode. The term \(T\Delta S\) is normalized to energy-per-mole units before subtraction.
- Avoid order-of-magnitude mistakes
- Prepare clean Gibbs-energy workflows
- Document conversion steps with traceability
Formulas (MathJax)
\[\Delta G = \Delta H - T\Delta S\]
\[\Delta H_{J/mol}=\Delta H_{input}\cdot f_{H}\]
\[\Delta S_{J/(mol\,K)}=\Delta S_{input}\cdot f_{S}\]
Formula symbol legend
- ΔH: enthalpy change
- ΔS: entropy change
- ΔG: Gibbs free energy
- T: absolute temperature in Kelvin
- fH, fS: unit conversion factors
Detailed examples
Example 1: ΔH = -45.5 kJ/mol → cal/mol gives \(-45.5\cdot1000/4.184\approx -10874\) cal/mol.
Example 2: ΔS = 120 J/(mol·K) → kJ/(mol·K) gives 0.120 kJ/(mol·K).
Example 3 (consistency check): ΔH = -120 kJ/mol, ΔS = -85 J/(mol·K), T = 298.15 K. Then \(T\Delta S\approx -25.34\) kJ/mol and \(\Delta G\approx -94.66\) kJ/mol (spontaneous).
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