How can enthalpy changes predict the feasibility of reactions?

Enthalpy changes can predict the feasibility of reactions by indicating whether a reaction is exothermic or endothermic.

Enthalpy is a measure of the total energy of a system. It is represented by the symbol H. When a chemical reaction occurs, there is often a change in the total energy of the system, which is referred to as the change in enthalpy, or ΔH. This change can either be positive, indicating that energy has been absorbed from the surroundings (an endothermic reaction), or negative, indicating that energy has been released to the surroundings (an exothermic reaction).

The feasibility of a reaction is often determined by the principle of minimum energy. This principle states that systems tend to evolve towards states of lower energy. Therefore, reactions that result in a decrease in the total energy of the system (exothermic reactions, where ΔH is negative) are generally more feasible than those that result in an increase in the total energy of the system (endothermic reactions, where ΔH is positive).

However, it's important to note that a negative ΔH alone does not guarantee that a reaction will occur. The reaction must also be thermodynamically favourable, meaning that the change in Gibbs free energy (ΔG) must be negative. The Gibbs free energy takes into account not only the change in enthalpy, but also the change in entropy (a measure of disorder) of the system.

In summary, while enthalpy changes can provide valuable insight into the feasibility of a reaction, they are just one piece of the puzzle. Other factors, such as entropy changes and temperature, also play crucial roles in determining whether a reaction will occur. Therefore, to fully predict the feasibility of a reaction, one must consider both the enthalpy and entropy changes, as well as the temperature at which the reaction is taking place.