What factors determine whether a chemical reaction is spontaneous or not?

Verified step by step guidance

1. Understand that the spontaneity of a chemical reaction is determined by the Gibbs free energy change (ΔG). A reaction is spontaneous if ΔG < 0 (negative).
2. Recall the formula for Gibbs free energy: $\Delta G\; =\; \Delta H\; -\; T\Delta S$, where ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy.
3. Analyze the role of enthalpy (ΔH): If ΔH is negative (exothermic reaction), it favors spontaneity. If ΔH is positive (endothermic reaction), it works against spontaneity.
4. Consider the role of entropy (ΔS): If ΔS is positive (increase in disorder), it favors spontaneity. If ΔS is negative (decrease in disorder), it works against spontaneity.
5. Evaluate the temperature (T): At higher temperatures, the TΔS term becomes more significant. This means that reactions with a positive ΔS are more likely to be spontaneous at higher temperatures, while reactions with a negative ΔS may require lower temperatures to be spontaneous.

Key Concepts

Gibbs Free Energy

Gibbs Free Energy (G) is a thermodynamic potential that helps predict whether a chemical reaction will occur spontaneously at constant temperature and pressure. A reaction is spontaneous if the change in Gibbs Free Energy (ΔG) is negative, indicating that the products have lower energy than the reactants. This concept integrates both enthalpy and entropy, providing a comprehensive criterion for spontaneity.

Enthalpy and Entropy

Enthalpy (H) is a measure of the total heat content of a system, while entropy (S) quantifies the degree of disorder or randomness. The relationship between these two properties is crucial in determining spontaneity. A reaction can be spontaneous if it releases heat (exothermic, ΔH < 0) or increases disorder (ΔS > 0), or both, as reflected in the Gibbs Free Energy equation: ΔG = ΔH - TΔS.

Temperature's Role

Temperature (T) plays a significant role in determining the spontaneity of a reaction, particularly through its influence on entropy. As temperature increases, the impact of entropy on Gibbs Free Energy becomes more pronounced. For reactions where entropy increases (ΔS > 0), higher temperatures can favor spontaneity, even if the reaction is endothermic (ΔH > 0), making temperature a critical factor in the spontaneity of chemical reactions.