What type of reaction typically results in a decrease in entropy?

Combination reactions generally result in a decrease in entropy because they involve the combination of two or more reactants to form a single product. Entropy, a measure of disorder or randomness in a system, tends to be lower in combinations since the number of gas molecules or particles typically decreases. For instance, when two gases combine to form a solid or liquid, the chaotic motion of the gas molecules is reduced, leading to more order and therefore a decrease in entropy.

Other types of reactions may have different effects on entropy. Endothermic and exothermic reactions do not inherently dictate changes in entropy, as these terms primarily describe heat transfer. Decomposition reactions, which involve a single compound breaking down into multiple products, usually lead to an increase in entropy due to the generation of more molecules and greater disorder. Thus, combination reactions are characteristic of a decrease in entropy compared to the other reaction types mentioned.