Introduction to Gibbs free energy | Applications of thermodynamics | AP Chemistry | Khan Academy

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Gibbs Free Energy is represented by G, with the formula for delta G being delta H minus (temperature in Kelvin times delta S), determining thermodynamic favorability based on the sign of delta G. A process is favored in the forward direction when delta G is less than zero, leading to spontaneous reactions, while delta G greater than zero indicates non-spontaneity in the forward direction.

Insights

  • Delta G determines whether a process is thermodynamically favorable (negative), unfavorable (positive), or at equilibrium (zero), based on the relationship between enthalpy (delta H), entropy (delta S), and temperature.
  • The standard state conditions for calculating delta G naught involve pure substances at specific pressures and concentrations, with the equilibrium point reached when delta G equals zero, indicating a balanced process.

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Recent questions

  • What is Gibbs Free Energy?

    The Gibbs Free Energy, denoted as G, represents the energy available to do work in a system at constant temperature and pressure. It is a thermodynamic potential that combines enthalpy and entropy to predict whether a reaction will be spontaneous or non-spontaneous.

  • How is delta G calculated?

    Delta G, the change in Gibbs Free Energy, is calculated using the formula delta G = delta H - (T * delta S), where delta H is the change in enthalpy, T is the temperature in Kelvin, and delta S is the change in entropy. This equation helps determine the spontaneity of a reaction based on the energy changes involved.

  • What does delta G less than zero indicate?

    When delta G is less than zero, it signifies that a process is favored in the forward direction, indicating thermodynamic favorability. This condition suggests that the reaction will occur spontaneously, releasing energy in the process.

  • What happens when delta G is greater than zero?

    If delta G is greater than zero, the process is favored in the reverse direction, indicating non-spontaneity in the forward direction. In this scenario, the reaction requires an input of energy to proceed, making it less likely to occur spontaneously.

  • What is the significance of delta G at equilibrium?

    At equilibrium, when delta G equals zero, the process is balanced, and there is no net change occurring. This state indicates that the forward and reverse reactions are proceeding at equal rates, resulting in a dynamic equilibrium. The standard state conditions for substances play a crucial role in determining the equilibrium state of a reaction.

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Summary

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Understanding Gibbs Free Energy in Thermodynamics

  • Gibbs Free Energy is represented by G, and the change in Gibbs Free Energy is denoted as delta G. The formula for delta G is delta H minus (temperature in Kelvin times delta S).
  • When delta G is less than zero, a process is favored in the forward direction, indicating thermodynamic favorability. This is often referred to as a spontaneous reaction in textbooks.
  • Conversely, when delta G is greater than zero, the process is favored in the reverse direction, indicating non-spontaneity in the forward direction.
  • At equilibrium, when delta G equals zero, the process is balanced. The standard state for substances involves pure solids or liquids under one atmosphere pressure, pure gases at one atmosphere pressure, and solutions at one Mueller concentration. Calculating delta G naught for a reaction involves using standard enthalpy and entropy changes.
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