Free Energy

Definition

Free energy is a thermodynamic potential that measures the work obtainable from a closed system at constant temperature and pressure. It helps in understanding the spontaneity of processes, as changes in free energy indicate whether a reaction can occur naturally without external intervention. The most commonly used forms are Gibbs free energy and Helmholtz free energy, which relate to different conditions of constant temperature and volume or pressure.

5 Must Know Facts For Your Next Test

1. A decrease in Gibbs free energy ( ext{ΔG} < 0) signifies that a reaction is spontaneous under constant temperature and pressure conditions.
2. Free energy is particularly useful in biochemical reactions to predict whether a metabolic process will proceed.
3. The relationship between enthalpy, entropy, and free energy is described by the equation ext{ΔG} = ext{ΔH} - T ext{ΔS}, where ext{ΔH} is the change in enthalpy, T is the absolute temperature, and ext{ΔS} is the change in entropy.
4. At equilibrium, the change in free energy for a system is zero ( ext{ΔG} = 0), indicating no net change or movement towards product or reactant.
5. Free energy can also be affected by changes in concentration of reactants or products, illustrating its role in chemical equilibrium.

Review Questions

• How does free energy relate to the spontaneity of reactions?
  • Free energy plays a crucial role in determining whether a reaction will occur spontaneously. If the change in Gibbs free energy ( ext{ΔG}) for a reaction is negative, it indicates that the reaction can proceed without additional energy input. This means that reactions with lower free energy are favored, leading to spontaneous processes that naturally move toward equilibrium.
• Discuss the differences between Gibbs and Helmholtz free energy in terms of their applications and conditions.
  • Gibbs free energy is used primarily for processes occurring at constant temperature and pressure, making it relevant for chemical reactions in open systems like biological processes. Helmholtz free energy, on the other hand, applies to systems at constant temperature and volume, often used in physical chemistry to describe systems with fixed volumes such as gases in closed containers. Both potentials help analyze energy transformations, but they cater to different experimental conditions.
• Evaluate how changes in temperature and concentration can impact free energy and spontaneity.
  • Changes in temperature can directly affect both entropy and enthalpy, thus influencing Gibbs free energy. For example, increasing temperature may favor endothermic reactions if the increase in entropy compensates for enthalpic costs. Additionally, alterations in concentration shift equilibrium positions according to Le Chatelier's principle, impacting free energy. An increase in reactant concentration typically reduces ext{ΔG}, promoting spontaneity by making reactions more favorable.

Related terms

Gibbs Free Energy:

A thermodynamic potential that indicates the maximum reversible work that can be performed by a thermodynamic system at constant temperature and pressure.

Helmholtz Free Energy: A thermodynamic potential that represents the amount of work obtainable from a closed system at constant temperature and volume.

Spontaneity: The tendency of a process to occur without outside intervention, often determined by the change in free energy during the process.