Gibbs Free Energy

Definition

Gibbs free energy is a thermodynamic potential that measures the maximum reversible work obtainable from a closed system at constant temperature and pressure. It is a crucial concept because it helps predict the direction of chemical reactions and phase transitions, determining whether a process will occur spontaneously based on changes in enthalpy and entropy.

5 Must Know Facts For Your Next Test

1. The Gibbs free energy change (∆G) can be used to determine the spontaneity of a reaction: if ∆G < 0, the reaction is spontaneous; if ∆G > 0, it is non-spontaneous.
2. At equilibrium, the Gibbs free energy is at its minimum, indicating that no net change occurs in the system.
3. The relationship between Gibbs free energy and enthalpy/entropy is expressed by the equation: $$ ext{G} = ext{H} - T ext{S}$$ where H is enthalpy, T is temperature, and S is entropy.
4. In chemical reactions, the Gibbs free energy can be used to calculate equilibrium constants through the relation: $$ ext{ΔG} = -RT ext{ln}(K)$$ where R is the gas constant and K is the equilibrium constant.
5. The concept of Gibbs free energy extends to solutions and mixtures, allowing for calculations related to chemical potential and phase behavior.

Review Questions

• How does Gibbs free energy relate to spontaneous processes and equilibrium in thermodynamics?
  • Gibbs free energy provides a criterion for spontaneity in thermodynamic processes. A reaction or process occurs spontaneously when the change in Gibbs free energy (∆G) is negative. At equilibrium, the Gibbs free energy reaches its minimum value, indicating that there are no further changes occurring in the system. This relationship highlights how Gibbs free energy serves as an essential link between thermodynamic stability and chemical reactivity.
• Discuss how changes in enthalpy and entropy contribute to Gibbs free energy and its significance in phase transitions.
  • Changes in enthalpy (∆H) and entropy (∆S) directly affect Gibbs free energy as described by the equation $$ ext{G} = ext{H} - T ext{S}$$. In phase transitions, such as melting or boiling, these changes can indicate whether a transition will occur under specific conditions. For instance, during melting, if the increase in entropy due to greater molecular disorder exceeds the enthalpic costs associated with breaking intermolecular bonds, ∆G will be negative, allowing the phase transition to happen spontaneously.
• Analyze how Gibbs free energy applies to chemical reactions and how it influences reaction spontaneity and equilibrium constants.
  • Gibbs free energy plays a critical role in chemical reactions by providing insights into their spontaneity and equilibrium states. The relationship between Gibbs free energy change (∆G) and equilibrium constants (K) shows that a reaction with a large negative ∆G will have a large K, indicating that products are favored at equilibrium. Conversely, a positive ∆G suggests reactants are favored. This analysis helps chemists understand not just whether reactions will occur but also how they might shift under varying conditions like temperature or pressure.

Related terms

Enthalpy: A measure of the total energy of a thermodynamic system, often used to determine heat changes during chemical reactions at constant pressure.

Entropy: A measure of the disorder or randomness in a system, which is vital for understanding the spontaneity of processes and the second law of thermodynamics.

Chemical Potential: The change in Gibbs free energy per change in the number of particles, reflecting how the Gibbs free energy varies with the composition of a system.