The equation for the formation of silicon tetrachloride from silicon and chlorine is (7.9) Si(s) + 2Cl₂(g) → SiCl₄(g) + 157 kcal b. Is the energy of the product higher or lower than the energy of the reactants?

The reaction given is exothermic, meaning it releases energy, specifically 157 kcal, as it proceeds from reactants to products. In exothermic reactions, the energy of the products is lower than that of the reactants because the excess energy is released into the surroundings, often in the form of heat.

Enthalpy change, represented as ΔH, quantifies the heat content of a system at constant pressure. In this reaction, the negative value of ΔH indicates that the products (SiCl₄) have a lower enthalpy than the reactants (Si and Cl₂), confirming that energy is released during the formation of silicon tetrachloride.

Thermodynamic stability refers to the relative energy levels of reactants and products in a chemical reaction. A product is considered thermodynamically stable if it has lower energy than the reactants, which is the case here, as the formation of SiCl₄ results in a more stable state due to the release of energy.