Gibb’s Free Energy

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.

  • 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.

Test Yourself

Assorted Multiple Choice
A constant current is passed through an electrolytic cell for 45.0 minutes, delivering a total charge of 8,100 Coulombs. How many moles of electrons were transferred during this process? (Faraday's constant = 96,485 C/mol e⁻)

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Gibb's Free Energy

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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: $\Delta G^\circ = \sum \Delta G^\circ_{\text{products}} - \sum \Delta G^\circ_{\text{reactants}}$

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