key term - Molar Gibbs energy

Definition

Molar Gibbs energy, also known as molar free energy, is the change in Gibbs free energy per mole of a substance during a chemical reaction or physical transformation. It is an important concept as it helps determine the spontaneity of reactions and the equilibrium position of chemical processes, linking the concepts of chemical potential and thermodynamics.

5 Must Know Facts For Your Next Test

1. Molar Gibbs energy is typically expressed in units of joules per mole (J/mol) and can provide insight into reaction feasibility at constant temperature and pressure.
2. A negative change in molar Gibbs energy (ΔG < 0) indicates that a process can occur spontaneously, while a positive change (ΔG > 0) suggests that the process is non-spontaneous.
3. At equilibrium, the molar Gibbs energy of the reactants equals that of the products, and ΔG is zero, meaning no net change occurs in the system.
4. The relationship between molar Gibbs energy and temperature can be represented by the equation ΔG = ΔH - TΔS, where ΔH is the change in enthalpy and ΔS is the change in entropy.
5. Molar Gibbs energy plays a critical role in determining phase transitions, as changes in temperature and pressure affect the stability of different phases.

Review Questions

• How does molar Gibbs energy influence the spontaneity of chemical reactions?
  • Molar Gibbs energy is key to understanding whether a chemical reaction will occur spontaneously. When the change in molar Gibbs energy (ΔG) for a reaction is negative, it indicates that the reaction can proceed without external input. This means that under standard conditions, reactions favoring lower energy states will tend to happen spontaneously, while those requiring energy input will not.
• Discuss how molar Gibbs energy relates to equilibrium constants in chemical reactions.
  • Molar Gibbs energy is directly connected to equilibrium constants through the equation ΔG = -RT ln(K), where R is the universal gas constant, T is the temperature, and K is the equilibrium constant. This equation indicates that a lower molar Gibbs energy corresponds to a larger equilibrium constant, suggesting that products are favored at equilibrium. Thus, by analyzing molar Gibbs energy changes, one can predict how far a reaction will proceed before reaching equilibrium.
• Evaluate how changes in temperature impact molar Gibbs energy and consequently affect phase transitions.
  • Changes in temperature can significantly influence molar Gibbs energy due to its dependence on both enthalpy (ΔH) and entropy (ΔS). As expressed in the equation ΔG = ΔH - TΔS, increasing temperature can lead to higher values of TΔS, which may make ΔG more negative for endothermic reactions. This shift can result in phase transitions; for instance, at higher temperatures, substances may favor a gaseous state over a solid or liquid state. Therefore, understanding this relationship helps predict when phase changes are likely to occur under varying thermal conditions.

Related terms

Gibbs Free Energy:

A thermodynamic potential that measures the maximum reversible work obtainable from a system at constant temperature and pressure.

Chemical Potential:

The change in Gibbs free energy of a system when an additional amount of a substance is added, reflecting how the energy of the system changes with composition.

Equilibrium Constant:

A ratio that expresses the relationship between the concentrations of products and reactants at equilibrium for a reversible reaction, directly related to the change in Gibbs free energy.