Gibbs Free Energy (ΔG) Calculator

Gibbs Free Energy (ΔG) Calculator

What is Gibbs Free Energy (ΔG)?

Gibbs Free Energy (ΔG) is a thermodynamic potential that measures the maximum amount of non-expansion work that can be extracted from a closed system at constant temperature and pressure. More importantly for chemists, it determines whether a chemical reaction will occur spontaneously under those conditions.

The Gibbs Free Energy change is calculated using the equation:

ΔG = ΔH - TΔS

Where:
• ΔG = Change in Gibbs Free Energy
• ΔH = Change in Enthalpy (heat absorbed or released)
• T = Absolute temperature (in Kelvin)
• ΔS = Change in Entropy (change in disorder or randomness)

The sign of ΔG tells us about spontaneity:
• ΔG < 0 (Negative): The reaction is spontaneous (favored to proceed).
• ΔG > 0 (Positive): The reaction is non-spontaneous (requires energy input to proceed).
• ΔG = 0: The system is at equilibrium.

Frequently Asked Questions

How do temperature, enthalpy, and entropy affect spontaneity?

The interplay between ΔH, ΔS, and T determines the sign of ΔG:
• If ΔH is negative (exothermic) and ΔS is positive (more disorder), ΔG will always be negative, and the reaction is always spontaneous.
• If ΔH is positive (endothermic) and ΔS is negative (less disorder), ΔG will always be positive, and the reaction is never spontaneous.
• If both ΔH and ΔS are negative, the reaction becomes spontaneous only at low temperatures (where the favorable ΔH term dominates).
• If both ΔH and ΔS are positive, the reaction becomes spontaneous only at high temperatures (where the favorable TΔS term dominates).

What does 'spontaneous' mean in chemistry?

In thermodynamics, "spontaneous" does not mean the reaction happens quickly. It only means that the reaction is thermodynamically favored and can proceed without a continuous external input of energy once it starts. A spontaneous reaction might still be very slow (like the rusting of iron) if its activation energy is high. Kinetics (reaction rates) is a separate field from thermodynamics (spontaneity).

Why are the units for ΔH and ΔS different (kJ vs J)?

Enthalpy changes (ΔH) are typically much larger in magnitude than entropy changes (ΔS). Therefore, ΔH is usually reported in kilojoules per mole (kJ/mol), while ΔS is reported in joules per mole per Kelvin (J/(mol·K)). It's crucial to convert them to the same energy unit (usually Joules) before using the ΔG equation, which this calculator does automatically.