Gibbs Free Energy

Definition

Gibbs free energy is a thermodynamic property that combines the concepts of enthalpy and entropy to determine the spontaneity and feasibility of a chemical process. It is a crucial factor in understanding the driving forces behind chemical reactions and phase changes.

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: $G = H - TS$.
2. The sign of the Gibbs free energy change ($\Delta G$) determines the spontaneity of a process: $\Delta G < 0$ for spontaneous processes, $\Delta G > 0$ for non-spontaneous processes, and $\Delta G = 0$ for processes at equilibrium.
3. Gibbs free energy is used to predict the feasibility of chemical reactions and phase changes, as well as to determine the direction of energy flow in a system.
4. In the context of phase diagrams, Gibbs free energy is used to determine the stable phases of a substance under different temperature and pressure conditions.
5. Gibbs free energy is a key factor in the dissolution process, as it determines the spontaneity and extent of solute dissolution based on the balance between enthalpy and entropy changes.

Review Questions

• Explain how Gibbs free energy relates to the concept of enthalpy and its role in determining the spontaneity of a chemical process.
  • Gibbs free energy combines the concepts of enthalpy and entropy to determine the spontaneity of a chemical process. Enthalpy represents the energy released or absorbed during a reaction, while entropy measures the disorder or randomness of the system. Gibbs free energy, defined as $G = H - TS$, takes both of these factors into account. If the change in Gibbs free energy ($\Delta G$) is negative, the process is spontaneous, as the decrease in free energy drives the system towards a more stable state. Conversely, if $\Delta G$ is positive, the process is non-spontaneous and requires the input of external energy to occur.
• Describe the role of Gibbs free energy in the context of phase diagrams and its influence on the dissolution process.
  • Gibbs free energy is a crucial factor in understanding phase diagrams and the dissolution process. In phase diagrams, the stable phases of a substance are determined by the region of lowest Gibbs free energy for a given temperature and pressure. As conditions change, the system will transition to the phase with the lowest free energy to achieve equilibrium. Similarly, in the dissolution process, Gibbs free energy is used to predict the spontaneity and extent of solute dissolution. If the change in Gibbs free energy for the dissolution process is negative, the process is spontaneous, and the solute will dissolve. If $\Delta G$ is positive, the dissolution is non-spontaneous, and the solute will not dissolve readily.
• Analyze how Gibbs free energy is related to chemical equilibrium and the concept of spontaneity, and explain how this relationship can be used to predict the direction and extent of a chemical reaction.
  • Gibbs free energy is intrinsically linked to the concept of chemical equilibrium and spontaneity. At equilibrium, the Gibbs free energy of the system is minimized, and $\Delta G = 0$. For a spontaneous process, $\Delta G < 0$, indicating that the system is moving towards a lower free energy state. Conversely, for a non-spontaneous process, $\Delta G > 0$, and the system requires an input of energy to proceed. By analyzing the sign and magnitude of $\Delta G$, one can predict the direction and extent of a chemical reaction. If $\Delta G$ is negative, the reaction will proceed spontaneously towards the products. If $\Delta G$ is positive, the reaction is non-spontaneous, and the reactants will be favored. The size of $\Delta G$ also indicates the driving force behind the reaction, with larger negative values corresponding to more favorable, spontaneous processes.

Related terms

Enthalpy: The total energy of a system, including the energy required to create the system (internal energy) and the work done to make room for it (pressure-volume work).

Entropy: A measure of the disorder or randomness of a system, representing the tendency of a system to become more disordered over time.

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