Calculate Gibbs free energy (ΔG), enthalpy change (ΔH), and entropy change (ΔS) to determine reaction spontaneity at constant temperature and pressure.
Gibbs Free Energy (ΔG)
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Reaction Spontaneity
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Standard Gibbs Energy (ΔG°)
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Entropy Contribution (-TΔS)
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Gibbs free energy is calculated using ΔG = ΔH - TΔS, where ΔH is enthalpy change, T is absolute temperature in Kelvin, and ΔS is entropy change. Make sure units are consistent (convert J to kJ if needed).
At equilibrium, there's no net change in the system and no driving force for the reaction to proceed in either direction. This corresponds to ΔG = 0, representing a balanced state between forward and reverse reactions.
Gibbs free energy predicts reaction spontaneity: ΔG < 0 means spontaneous (favorable), ΔG > 0 means non-spontaneous (requires energy input), and ΔG = 0 indicates equilibrium.
Check the sign of ΔG: negative values indicate spontaneous reactions that can occur naturally, while positive values indicate non-spontaneous reactions requiring external energy input to proceed.
ΔG° is the standard Gibbs free energy change under standard conditions (1 atm, 25°C), while ΔG accounts for actual reaction conditions including temperature and concentrations of reactants and products.
The Gibbs free energy equation is derived from thermodynamic principles that require absolute temperature. Kelvin is the absolute temperature scale starting at absolute zero, ensuring accurate calculations.