Free Energy

Definition

Free energy is a measure of the useful work that can be extracted from a thermodynamic system. It represents the amount of energy available to do work while accounting for the system's entropy and the constraints imposed by the environment. This concept is crucial in understanding chemical reactions, equilibria, and the energy changes associated with various processes in chemistry and biochemistry.

5 Must Know Facts For Your Next Test

1. Free energy is the maximum amount of work that can be extracted from a system at constant temperature and pressure.
2. The change in free energy (ΔG) determines the spontaneity and feasibility of a chemical reaction, with a negative ΔG indicating a spontaneous and favorable reaction.
3. The Hammond Postulate states that the transition state of a reaction resembles the structure of the reactant or product that is closest in free energy.
4. In metabolism, the hydrolysis of ATP to ADP and inorganic phosphate is a highly exergonic reaction that provides the energy for many cellular processes.
5. The free energy change of a reaction is influenced by both the enthalpy and entropy changes, as described by the equation ΔG = ΔH - TΔS.

Review Questions

• Explain how the concept of free energy is used to describe the equilibrium of a chemical reaction.
  • The free energy change (ΔG) of a reaction determines the position of equilibrium. At equilibrium, the free energy of the system is minimized, and the change in free energy is zero (ΔG = 0). If ΔG is negative, the reaction is spontaneous and favored to proceed in the forward direction. Conversely, a positive ΔG indicates that the reaction is non-spontaneous and will proceed in the reverse direction. The magnitude of ΔG also provides information about the extent of the reaction and the relative stability of the reactants and products.
• Describe the role of free energy in the Hammond Postulate and its implications for reaction mechanisms.
  • The Hammond Postulate states that the transition state of a reaction resembles the structure of the reactant or product that is closest in free energy. This means that the transition state will be more similar to the species (reactant or product) that is closer in free energy to the transition state. This has important implications for understanding reaction mechanisms, as the transition state structure can provide insights into the relative stabilities of intermediates and the overall energetics of the reaction pathway.
• Analyze the significance of free energy changes in the context of metabolism and biochemical energy transformations.
  • In the study of metabolism, the concept of free energy is crucial for understanding the energy requirements and energy-releasing processes that sustain life. The hydrolysis of ATP to ADP and inorganic phosphate is a highly exergonic reaction, meaning it releases a large amount of free energy. This free energy is then used to drive a wide range of essential cellular processes, such as active transport, muscle contraction, and biosynthesis. Additionally, the coupling of exergonic and endergonic reactions, where the free energy released from one process is used to drive another, is a fundamental principle of metabolism and allows for the efficient utilization of biochemical energy.

Related terms

Gibbs Free Energy: Gibbs free energy is 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.

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

Entropy: Entropy is a measure of the disorder or randomness of a system, and it is a key factor in determining the spontaneity and direction of a process.