Gibbs Free Energy

Definition

Gibbs free energy 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 measure of the useful work that can be extracted from a system at constant temperature and pressure.

5 Must Know Facts For Your Next Test

1. Gibbs free energy is defined as the sum of a system's enthalpy and the product of its entropy and absolute temperature: $G = H - TS$, where $G$ is Gibbs free energy, $H$ is enthalpy, $T$ is absolute temperature, and $S$ is entropy.
2. A negative value of Gibbs free energy indicates a spontaneous and favorable process, while a positive value indicates a non-spontaneous and unfavorable process.
3. Gibbs free energy is a key factor in determining the direction and feasibility of phase changes, as it accounts for both the energy changes (enthalpy) and the disorder changes (entropy) during the transition.
4. In the context of phase changes, a decrease in Gibbs free energy corresponds to a spontaneous transition from a less stable to a more stable phase, such as the melting of ice or the boiling of water.
5. On a microscopic scale, Gibbs free energy is related to the disorder and randomness of a system, as it incorporates the entropy term. Processes that increase the overall disorder of a system tend to have a lower Gibbs free energy and are therefore more likely to occur spontaneously.

Review Questions

• Explain how Gibbs free energy is used to determine the spontaneity of a chemical process.
  • Gibbs free energy is a measure of the useful work that can be extracted from a system at constant temperature and pressure. A negative value of Gibbs free energy indicates that a process is spontaneous and favorable, as the system is moving towards a state of lower free energy. Conversely, a positive value of Gibbs free energy indicates a non-spontaneous and unfavorable process, as the system would require the input of external energy to proceed. The sign and magnitude of Gibbs free energy, therefore, provide a clear indication of the spontaneity and feasibility of a chemical process.
• Describe the relationship between Gibbs free energy, enthalpy, and entropy in the context of phase changes.
  • Gibbs free energy is the sum of a system's enthalpy and the product of its entropy and absolute temperature: $G = H - TS$. During a phase change, such as the melting of ice or the boiling of water, the system experiences changes in both energy (enthalpy) and disorder (entropy). A decrease in Gibbs free energy corresponds to a spontaneous transition from a less stable to a more stable phase, as the system moves towards a state of lower free energy. This is because the increase in entropy during the phase change outweighs the increase in enthalpy, resulting in a net decrease in Gibbs free energy and a spontaneous process.
• Explain how Gibbs free energy is related to the microscopic disorder of a system and its impact on the spontaneity of processes.
  • On a microscopic scale, Gibbs free energy is closely related to the disorder and randomness of a system, as it incorporates the entropy term. Processes that increase the overall disorder of a system, and therefore its entropy, tend to have a lower Gibbs free energy and are more likely to occur spontaneously. This is because the increase in entropy outweighs any increase in enthalpy, resulting in a net decrease in Gibbs free energy. Conversely, processes that decrease the disorder of a system, and therefore its entropy, will have a higher Gibbs free energy and are less likely to occur spontaneously without the input of external energy. The relationship between Gibbs free energy and entropy, therefore, is a key factor in determining the spontaneity and feasibility of processes on a microscopic scale.

Related terms

Enthalpy: The total energy of a system, including both internal energy and the work done by or on the system due to changes in pressure and volume.

Entropy: A measure of the disorder or randomness of a system, which increases as a system moves towards a more disordered state.

Spontaneity: The tendency of a process to occur naturally without the input of external energy, driven by the system's tendency to minimize its Gibbs free energy.