Free energy

Definition

Free energy is a thermodynamic quantity that represents the amount of work obtainable from a system at constant temperature and pressure. It combines the system's internal energy with its entropy, giving insight into the spontaneity of a process. In the context of chemical reactions, free energy helps predict whether a reaction will occur spontaneously, linking the concepts of thermodynamics and kinetics.

5 Must Know Facts For Your Next Test

1. Free energy changes determine if a reaction is spontaneous; if the change in free energy ($$\Delta G$$) is negative, the reaction can proceed without external input.
2. The relationship between free energy and equilibrium is crucial; at equilibrium, $$\Delta G$$ is zero, indicating no net change in the concentrations of reactants and products.
3. Temperature has a significant impact on free energy; as temperature increases, the effect of entropy on free energy changes becomes more pronounced.
4. The standard free energy change ($$\Delta G^{\circ}$$) provides a reference point for comparing different reactions under standard conditions.
5. Changes in free energy are linked to both kinetic and thermodynamic parameters, allowing chemists to analyze not just if reactions will occur but how quickly they will proceed.

Review Questions

• How does free energy relate to spontaneity in chemical reactions?
  • Free energy is crucial in determining whether a chemical reaction will occur spontaneously. If the change in free energy ($$\Delta G$$) for a reaction is negative, it indicates that the reaction can proceed without needing additional energy input. Conversely, if $$\Delta G$$ is positive, the reaction is non-spontaneous and requires external energy to occur.
• Discuss the importance of Gibbs free energy in understanding chemical equilibria.
  • Gibbs free energy plays a central role in understanding chemical equilibria because it quantitatively describes the relationship between reactants and products. At equilibrium, the Gibbs free energy change ($$\Delta G$$) is zero, meaning that the forward and reverse reactions occur at equal rates. This equilibrium condition provides insight into how changes in concentration or temperature can shift the balance between products and reactants.
• Evaluate how activation energy and free energy are interconnected in predicting reaction behavior.
  • Activation energy and free energy are interconnected concepts that together provide a complete picture of reaction behavior. While free energy determines the spontaneity of a reaction, activation energy represents the barrier that must be overcome for reactants to be transformed into products. Understanding both allows chemists to predict not just whether a reaction can happen spontaneously (via free energy) but also how fast it will happen (considering activation energy), highlighting the relationship between kinetics and thermodynamics.

Related terms

Gibbs free energy: A specific form of free energy that accounts for enthalpy and entropy changes at constant temperature and pressure, expressed as $$G = H - TS$$.

Activation energy: The minimum energy required for a chemical reaction to occur, representing the barrier that reactants must overcome to transform into products.

Equilibrium constant: A numerical value that expresses the ratio of the concentrations of products to reactants at equilibrium, influenced by the free energy change of the reaction.