Free Energy Change

Definition

Free energy change refers to the difference in energy available to do work during a chemical reaction, taking into account both enthalpy and entropy. It provides a measure of spontaneity for a reaction; if the free energy change is negative, the reaction can occur spontaneously, whereas a positive value indicates that the reaction is non-spontaneous under standard conditions. Understanding free energy change is crucial for predicting the behavior of oxidation and reduction processes.

5 Must Know Facts For Your Next Test

1. The formula for calculating free energy change is $$\Delta G = \Delta H - T\Delta S$$, where $$\Delta G$$ is free energy change, $$\Delta H$$ is enthalpy change, $$T$$ is temperature in Kelvin, and $$\Delta S$$ is entropy change.
2. A negative free energy change (\$\Delta G < 0$\) indicates that the reaction can proceed spontaneously, while a positive change (\$\Delta G > 0$\) suggests that external energy input is required.
3. In oxidation-reduction reactions, changes in free energy are linked to the transfer of electrons and can be quantified using standard electrode potentials.
4. The concept of free energy change helps in understanding equilibrium; at equilibrium, \$\Delta G = 0$\, meaning no net change occurs in reactants and products over time.
5. Factors such as temperature, concentration of reactants/products, and pressure can affect free energy change, influencing reaction spontaneity.

Review Questions

• How does free energy change relate to the spontaneity of oxidation-reduction reactions?
  • Free energy change is directly linked to whether an oxidation-reduction reaction can occur spontaneously. If the free energy change (\$\Delta G$\) is negative, it indicates that the reaction can proceed without additional energy input. This relationship helps in understanding redox reactions where electron transfer occurs; spontaneous reactions often involve favorable changes in both enthalpy and entropy that contribute to a negative \$\Delta G$\.
• Discuss how enthalpy and entropy contribute to free energy change in redox reactions.
  • Enthalpy and entropy are critical components in determining free energy change for redox reactions. Enthalpy reflects heat content and can indicate if a reaction releases or absorbs heat. Entropy measures disorder; an increase in entropy usually favors spontaneity. The interplay between these two factors determines whether \$\Delta G$\ is negative or positive. For example, a highly exothermic reaction may have a favorable \$\Delta G$\ even if it has a slight decrease in entropy.
• Evaluate how variations in temperature might affect free energy change and consequently the spontaneity of a reaction.
  • Temperature plays a significant role in calculating free energy change since it directly impacts the \$T\Delta S$\ term in the equation \$\Delta G = \Delta H - T\Delta S$\. As temperature increases, the influence of entropy becomes more pronounced. A reaction with a positive entropy change may become spontaneous at higher temperatures even if it’s endothermic. Thus, understanding how temperature shifts affect both enthalpy and entropy allows chemists to predict changes in spontaneity under different conditions.

Related terms

Enthalpy: A measure of the total heat content of a system, reflecting the internal energy plus the product of pressure and volume.

Entropy: A measure of the disorder or randomness in a system, which influences the spontaneity of reactions.

Gibbs Free Energy: A thermodynamic potential that represents the maximum reversible work obtainable from a system at constant temperature and pressure, often used to determine free energy change.