What is a reversible reaction?

A reversible reaction is one in which the products of the reaction can react to form the original reactants, meaning the reaction can proceed in both the forward and reverse directions. In such reactions, the system reaches a state of equilibrium where the rate of the forward reaction equals the rate of the reverse reaction, allowing both processes to occur simultaneously.

This characteristic allows reversible reactions to be driven towards either the reactants or products, depending on conditions such as concentration, temperature, and pressure. Examples of reversible reactions include the synthesis of ammonia from nitrogen and hydrogen gases, as well as the formation of ester from an alcohol and a carboxylic acid.

The other choices highlight aspects that do not define a reversible reaction. For instance, a unidirectional reaction can only proceed in one direction, while the requirement of a catalyst does not affect the reversibility of a reaction; it only changes the speed at which equilibrium is reached. Additionally, the production of gases does not inherently make a reaction reversible. The defining feature of reversibility is the ability to proceed in either direction.