Ammonium nitrate is dangerous because it decomposes (sometimes explosively) when heated: (a) Using the data in Appendix B, show that this reaction is spontaneous at 25 °C.

Key Concepts

Gibbs Free Energy

Gibbs Free Energy (G) is a thermodynamic potential that helps predict whether a reaction will occur spontaneously at constant temperature and pressure. A reaction is spontaneous if the change in Gibbs Free Energy (ΔG) is negative. 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 (ΔH) is a measure of the total heat content of a system, while entropy (ΔS) quantifies the degree of disorder or randomness in a system. For a reaction to be spontaneous, the increase in entropy must outweigh the enthalpy change at a given temperature. Understanding how these two factors interact is crucial for analyzing the spontaneity of chemical reactions.

Temperature's Role in Spontaneity

Temperature plays a critical role in determining the spontaneity of a reaction. As temperature increases, the TΔS term in the Gibbs Free Energy equation becomes more significant. This means that reactions with a positive entropy change can become spontaneous at higher temperatures, even if they are endothermic (positive ΔH) at lower temperatures.