$ΔG$

Definition

$ΔG$, or Gibbs free energy change, is a thermodynamic quantity that combines the concepts of energy, entropy, and temperature to determine the spontaneity and feasibility of a chemical process. It is a crucial factor in understanding the potential, free energy, and equilibrium of a system.

5 Must Know Facts For Your Next Test

1. $ΔG$ is defined as the change in Gibbs free energy, which is a function of the system's enthalpy ($ΔH$) and entropy ($ΔS$) changes, as well as the absolute temperature ($T$) of the system.
2. The equation for $ΔG$ is $ΔG = ΔH - TΔS$, where a negative $ΔG$ value indicates a spontaneous process, and a positive $ΔG$ value indicates a non-spontaneous process.
3. The sign of $ΔG$ determines the spontaneity of a process: a negative $ΔG$ means the process is spontaneous, a positive $ΔG$ means the process is non-spontaneous, and a $ΔG$ of zero indicates the process is at equilibrium.
4. The magnitude of $ΔG$ determines the extent of the process: the more negative the $ΔG$, the more favorable the process and the greater the driving force for the reaction to occur.
5. In the context of equilibrium, $ΔG = 0$ at the equilibrium state, indicating that the forward and reverse reactions are occurring at the same rate, and the system is in a state of balance.

Review Questions

• Explain how $ΔG$ is related to the spontaneity of a chemical process.
  • The sign of $ΔG$ determines the spontaneity of a chemical process. If $ΔG$ is negative, the process is spontaneous and will occur naturally without the input of external energy. If $ΔG$ is positive, the process is non-spontaneous and will not occur naturally. A $ΔG$ of zero indicates the process is at equilibrium, where the forward and reverse reactions are occurring at the same rate.
• Describe the relationship between $ΔG$, $ΔH$, and $ΔS$ as expressed in the equation $ΔG = ΔH - TΔS$.
  • The equation $ΔG = ΔH - TΔS$ shows that the Gibbs free energy change ($ΔG$) is a function of both the enthalpy change ($ΔH$) and the entropy change ($ΔS$) of the system, as well as the absolute temperature ($T$). Enthalpy represents the energy released or absorbed during a reaction, while entropy represents the change in disorder or randomness. The combination of these factors determines the spontaneity and feasibility of a chemical process.
• Analyze how the value of $ΔG$ can be used to predict the equilibrium state of a system.
  • At equilibrium, the Gibbs free energy change ($ΔG$) is zero, indicating that the forward and reverse reactions are occurring at the same rate, and the system is in a state of balance. If $ΔG$ is negative, the process is spontaneous and will proceed towards the products. If $ΔG$ is positive, the process is non-spontaneous and will not occur naturally. The magnitude of $ΔG$ also provides information about the driving force and extent of the reaction, with more negative values indicating a greater tendency for the reaction to occur.

Related terms

Enthalpy ($ΔH$): The total energy released or absorbed during a chemical reaction, including the energy required to break and form chemical bonds.

Entropy ($ΔS$): A measure of the disorder or randomness of a system, which increases as a system moves towards a more probable state.

Spontaneity:

The tendency of a process to occur naturally without the input of external energy, driven by the system's desire to reach a state of lower free energy.