Gibbs Free Energy Calculator
Calculate ΔG and interpret spontaneity.
Solve ΔG = ΔH − TΔS for any variable, and read off the spontaneity, the equilibrium constant, and the crossover temperature where the sign of ΔG flips. ΔH in kJ/mol and ΔS in J/(mol·K) are reconciled automatically.
A negative ΔG means the forward reaction is thermodynamically favoured; it says nothing about how fast the reaction goes.
How to Use the Gibbs Free Energy Calculator
1
Choose the unknown. Select ΔG, ΔH, ΔS, or the temperature at which a given ΔG occurs.
2
Enter the thermodynamic data. Type the known values with their units; kJ/mol for ΔH and ΔG and J/(mol·K) for ΔS are reconciled automatically.
3
Read spontaneity and crossover. The result reports the value, whether the process is spontaneous, the equilibrium constant, and the temperature where the sign of ΔG flips.
What is the Gibbs Free Energy Calculator?
The Gibbs free energy calculator evaluates ΔG = ΔH - TΔS and interprets the result: negative ΔG means a spontaneous process, positive means non-spontaneous, and zero means equilibrium. Temperature is handled in Kelvin with automatic conversion from Celsius.
The most useful output is often the crossover temperature T = ΔH/ΔS, where a reaction switches between spontaneous and non-spontaneous. The calculator reports it whenever the signs of ΔH and ΔS allow one to exist.
Common Uses
- Determine if a reaction is spontaneous at a given temperature
- Find the temperature where ΔG changes sign
- Relate enthalpy and entropy contributions
- Check thermodynamics homework answers
How to Solve It by Hand
Manual calculation is still important: identify the known variables, convert units before substitution, apply the equation, and check whether the result is chemically reasonable. The most common mistakes are inconsistent units, constants rounded too early, and skipping the interpretation step.
Practice Prompt
Try changing the default values and ask the lower-right chemistry chat why the result increased or decreased. That turns the calculator from a number machine into a study loop.
ΔG = ΔH - TΔS. A negative ΔG means the process is spontaneous (exergonic) in the forward direction, positive means non-spontaneous, and zero means the system is at equilibrium.
ΔH is normally tabulated in kJ/mol while ΔS is in J/(mol·K). Subtracting them directly is the single most common error in thermodynamics problems — one has to be converted by a factor of 1000 first. This calculator reconciles them automatically.
When ΔH and ΔS share a sign, the sign of ΔG flips at T = ΔH/ΔS. Below that temperature an exothermic, entropy-lowering reaction is spontaneous; above it, it is not. When the signs differ, no crossover exists and the outcome is temperature-independent.
ΔG° = -RT ln K, so K = e^(-ΔG°/RT). A ΔG° of about -6 kJ/mol at 298 K corresponds to K near 11, while -40 kJ/mol gives K near 10⁷.
No. Thermodynamics says whether a reaction is favoured, not how fast it goes. Diamond converting to graphite has a negative ΔG but an activation barrier so high the rate is effectively zero.