Gibb’s Free Energy
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Core Concept
Gibbs Free Energy is the maximum amount of work that a system can perform at constant temperature and pressure.
The sign of $\Delta G$ determines spontaneity:
$\Delta G < 0$ (Negative): The reaction is spontaneous (favorable).
$\Delta G > 0$ (Positive): The reaction is non-spontaneous (unfavorable).
$\Delta G = 0$: The system is at equilibrium.
Practice Tips
ΔG predicts spontaneity: ΔG < 0 means spontaneous.
Temperature plays a critical role in determining ΔG when ΔS ≠ 0.
Gibbs Free Energy is linked to equilibrium constants and the feasibility of reactions.
The Gibbs Free Energy Equation
The change in Gibbs Free Energy (ΔG) is given by: ΔG = ΔH − TΔS
Where:
ΔG: Change in Gibbs Free Energy.
ΔH: Enthalpy change (J/mol).
T: Temperature (Kelvin).
ΔS: Entropy change (J/K·mol).
What Does ΔG Tell Us?
Spontaneous Reaction: ΔG < 0 (negative)
The reaction occurs without external energy input.
Non-Spontaneous Reaction: ΔG > 0 (positive)
The reaction requires energy input to proceed.
Equilibrium: ΔG=0
The system is in a state of balance.
Factors Affecting Gibbs Free Energy
Enthalpy (ΔH):
Represents heat changes in a reaction.
Exothermic reactions (ΔH<0) tend to favor spontaneity.
Entropy (ΔS):
Represents disorder or energy dispersal.
Reactions that increase entropy (ΔS>0) tend to be spontaneous.
Temperature (T):
High temperatures amplify the effect of TΔS.
For reactions with ΔS>0, higher temperatures favor spontaneity.
Standard Gibbs Free Energy (ΔG)
Definition: Gibbs Free Energy change under standard conditions (25°C, 1 atm, 1 M concentrations).
Formula: $\Delta G^\circ = \sum \Delta G^\circ_{\text{products}} - \sum \Delta G^\circ_{\text{reactants}}$