Oxygen can be converted into ozone by the action of lightning or electric sparks: 3 O2(g) ⇌ 2 O3(g) For this reaction, ∆H = +69kcal/mol (+285 kj/mol) and K = 2.68 x 10^-29 at 25 °C. Is the reaction exothermic or endothermic?

Endothermic reactions absorb heat from their surroundings, resulting in a positive change in enthalpy (∆H > 0). Conversely, exothermic reactions release heat, leading to a negative change in enthalpy (∆H < 0). In this case, since the reaction has a positive ∆H of +69 kcal/mol, it indicates that the reaction is endothermic.

Enthalpy is a thermodynamic property that reflects the total heat content of a system. It is often used to determine the heat absorbed or released during a chemical reaction. The sign and magnitude of ∆H provide insight into whether a reaction is endothermic or exothermic, with positive values indicating heat absorption and negative values indicating heat release.

The equilibrium constant (K) quantifies the ratio of the concentrations of products to reactants at equilibrium for a reversible reaction. A very small K value, such as 2.68 x 10^-29, suggests that at equilibrium, the reactants (O2) are favored over the products (O3), indicating that the formation of ozone is not favored under standard conditions, despite the reaction being endothermic.