Gibbs Free Energy of Reaction Calculator

The Master Equation of Thermodynamics

Will a chemical reaction happen on its own?

For over a century, chemists debated what made a reaction "spontaneous." Some thought all reactions that released heat were spontaneous, but this didn't explain why ice spontaneously melts into water (which absorbs heat).

The American physicist J. Willard Gibbs solved this by proving that spontaneity is a tug-of-war between two different forces: Enthalpy (Heat) and Entropy (Chaos). He combined them into a single metric known as Gibbs Free Energy ($\Delta G$).

The Two Forces

1. Enthalpy ($\Delta H$): The universe is lazy; it prefers things to be in a low energy state. Exothermic reactions (negative $\Delta H$) that release heat are favorable.
2. Entropy ($\Delta S$): The universe is messy; it prefers chaos. Reactions that increase disorder (positive $\Delta S$, like a solid dissolving into a liquid) are favorable.

Temperature ($T$) acts as the multiplier for Entropy. At extremely high temperatures, chaos rules, and the Entropy term overpowers the Heat term.

The Gibbs Equation

The Spontaneity Rule

• If $\Delta G < 0$ (Negative): The reaction is Spontaneous. It will happen without any outside help.
• If $\Delta G > 0$ (Positive): The reaction is Non-Spontaneous. It will never happen unless you force it to.
• If $\Delta G = 0$: The reaction is perfectly at equilibrium.