Question 1

What does Gibbs free energy tell us?

Accepted Answer

Gibbs free energy (ΔG) predicts reaction spontaneity at constant temperature and pressure. ΔG < 0: spontaneous (exergonic). ΔG > 0: non-spontaneous (endergonic). ΔG = 0: at equilibrium.

Question 2

Why are the units different for ΔH and ΔS?

Accepted Answer

ΔH is typically in kJ/mol, while ΔS is in J/(mol·K). When using ΔG = ΔH - TΔS, you must convert to consistent units. This calculator converts ΔS from J to kJ by dividing by 1000.

Question 3

What is the equilibrium temperature?

Accepted Answer

The equilibrium temperature is where ΔG = 0, meaning ΔH = TΔS, so T = ΔH/ΔS. Above or below this temperature, the reaction may switch between spontaneous and non-spontaneous.

Question 4

Can a reaction with positive ΔH be spontaneous?

Accepted Answer

Yes, if ΔS is positive and large enough. At high temperatures, the TΔS term can overcome ΔH, making ΔG negative. Example: melting ice is endothermic but spontaneous above 0°C.

Gibbs Free Energy Calculator

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