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

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1. 1. The spontaneity of a chemical reaction is determined by two main factors: the change in enthalpy (ΔH) and the change in entropy (ΔS).
2. 2. The change in enthalpy (ΔH) refers to the total energy change of the system. If the reaction releases energy (exothermic), ΔH is negative and the reaction is more likely to be spontaneous. If the reaction absorbs energy (endothermic), ΔH is positive and the reaction is less likely to be spontaneous.
3. 3. The change in entropy (ΔS) refers to the change in disorder or randomness. If the reaction results in an increase in disorder (positive ΔS), it is more likely to be spontaneous. If the reaction results in a decrease in disorder (negative ΔS), it is less likely to be spontaneous.
4. 4. However, both these factors are considered together in the Gibbs free energy equation: ΔG = ΔH - TΔS. If ΔG is negative, the reaction is spontaneous. If ΔG is positive, the reaction is non-spontaneous.
5. 5. Temperature (T) also plays a role in determining the spontaneity of a reaction. At high temperatures, the entropy term (TΔS) can dominate, making reactions with positive ΔS but positive ΔH spontaneous.

Key Concepts

Gibbs Free Energy

Gibbs Free Energy (G) is a thermodynamic potential that helps predict the spontaneity of a chemical reaction. A reaction is spontaneous if the change in Gibbs Free Energy (ΔG) is negative, indicating that the process can occur without external energy input. The relationship is given by the equation ΔG = ΔH - TΔS, where ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy.

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. A spontaneous reaction typically involves a decrease in enthalpy (exothermic) or an increase in entropy. Understanding how these two factors interact is crucial for determining the overall spontaneity of a reaction, as they contribute to the Gibbs Free Energy change.

Temperature's Role

Temperature plays a significant role in determining the spontaneity of a reaction, as it affects both enthalpy and entropy. The term TΔS in the Gibbs Free Energy equation shows that at higher temperatures, the impact of entropy becomes more pronounced. This means that reactions with a positive ΔS can become spontaneous at elevated temperatures, even if they are endothermic (positive ΔH).