Standard Gibbs Free Energy Change

Definition

The standard Gibbs free energy change is a thermodynamic quantity that represents the maximum amount of non-expansion work that can be extracted from a chemical or physical process at constant temperature and pressure. It is a crucial concept in understanding the spontaneity and feasibility of chemical reactions and physical transformations.

5 Must Know Facts For Your Next Test

1. The standard Gibbs free energy change, denoted as $\Delta G^\circ$, is the change in Gibbs free energy under standard conditions (typically 25°C and 1 atm pressure).
2. A negative value of $\Delta G^\circ$ indicates that the process is spontaneous and releases free energy, while a positive value indicates that the process is non-spontaneous and requires the input of free energy.
3. The standard Gibbs free energy change is related to the equilibrium constant ($K_\text{eq}$) of a reaction through the equation: $\Delta G^\circ = -RT\ln K_\text{eq}$, where $R$ is the universal gas constant and $T$ is the absolute temperature.
4. The sign and magnitude of $\Delta G^\circ$ determine the feasibility and direction of a chemical reaction or physical transformation, with spontaneous processes having $\Delta G^\circ < 0$ and non-spontaneous processes having $\Delta G^\circ > 0$.
5. The standard Gibbs free energy change is a key factor in determining the position of chemical equilibrium, as it reflects the driving force for a reaction to proceed in the forward or reverse direction.

Review Questions

• Explain how the standard Gibbs free energy change is related to the spontaneity of a chemical reaction.
  • The sign of the standard Gibbs free energy change, $\Delta G^\circ$, determines the spontaneity of a chemical reaction. If $\Delta G^\circ$ is negative, the reaction is spontaneous and will occur naturally, releasing free energy. Conversely, if $\Delta G^\circ$ is positive, the reaction is non-spontaneous and requires the input of free energy to proceed. The magnitude of $\Delta G^\circ$ also reflects the driving force for the reaction, with larger negative values indicating a greater tendency for the reaction to occur spontaneously.
• Describe the relationship between the standard Gibbs free energy change and the equilibrium constant of a chemical reaction.
  • The standard Gibbs free energy change, $\Delta G^\circ$, is related to the equilibrium constant, $K_\text{eq}$, of a chemical reaction through the equation $\Delta G^\circ = -RT\ln K_\text{eq}$. This relationship allows us to determine the feasibility and direction of a reaction based on the value of $\Delta G^\circ$. If $\Delta G^\circ$ is negative, the reaction will proceed spontaneously towards equilibrium, and the equilibrium constant will be greater than 1. Conversely, if $\Delta G^\circ$ is positive, the reaction will be non-spontaneous, and the equilibrium constant will be less than 1.
• Explain how the standard Gibbs free energy change can be used to determine the position of chemical equilibrium.
  • The standard Gibbs free energy change, $\Delta G^\circ$, is a key factor in determining the position of chemical equilibrium. At equilibrium, the Gibbs free energy of the system is minimized, and the forward and reverse reaction rates are equal. The sign and magnitude of $\Delta G^\circ$ reflect the driving force for the reaction to proceed in the forward or reverse direction. If $\Delta G^\circ$ is negative, the reaction will be spontaneous and proceed towards the products, resulting in an equilibrium with a high product concentration. If $\Delta G^\circ$ is positive, the reaction will be non-spontaneous, and the equilibrium will favor the reactants.

Related terms

Gibbs Free Energy: A thermodynamic potential that combines the internal energy of a system with the work done by or on the system due to changes in pressure and volume, as well as the entropy of the system.

Spontaneity: The tendency of a process to occur naturally without the input of external energy, as determined by the sign of the Gibbs free energy change.

Chemical Equilibrium: The state where the forward and reverse reaction rates are equal, resulting in no net change in the concentrations of reactants and products over time.