Chemical Equilibrium - SS2 Chemistry Past Questions and Answers - page 1

A reversible reaction is a chemical reaction that can proceed in both the forward and reverse directions. It means that products can react with each other to form reactants, and reactants can react to form products. In a reversible reaction, there is an equilibrium state where the concentrations of reactants and products remain constant over time.

On the other hand, an irreversible reaction is a chemical reaction that proceeds in only one direction, and the conversion of reactants into products is complete. The reactants are entirely consumed, and the reaction cannot revert back to the original reactants.

Example of a reversible reaction: The Haber-Bosch process for ammonia synthesis:

N2(g) + 3H2(g) ⇌ 2NH3(g)

In this reaction, nitrogen gas (N2) and hydrogen gas (H2) react to form ammonia gas (NH3). However, ammonia can also decompose back into nitrogen and hydrogen under certain conditions.

Example of an irreversible reaction: Combustion of methane:

CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)

In this reaction, methane gas (CH4) reacts with oxygen gas (O2) to form carbon dioxide (CO2) and water (H2O). The combustion of methane is an irreversible process, and it proceeds in only one direction.

Dynamic equilibrium is a state reached in a reversible reaction when the rates of the forward and reverse reactions are equal. In dynamic equilibrium, the concentrations of reactants and products remain constant over time, but the reactions continue to occur simultaneously. It is important to note that dynamic equilibrium does not imply that the reactants and products are present in equal amounts, but rather that their concentrations are stable.

To reach dynamic equilibrium, certain conditions must be met:

a.    A closed system: The reaction must occur in a closed system where no reactants or products can enter or leave the system. This ensures that the total amount of matter remains constant throughout the process.

b.    Reversible reaction: The reaction must be reversible, meaning it can proceed in both the forward and reverse directions. This allows the establishment of equilibrium between the reactants and products.

c.     Constant temperature: The reaction must occur at a constant temperature. Temperature affects the rates of the forward and reverse reactions, and a stable temperature ensures that the rates remain equal at equilibrium.

d.    Sufficient time: The system needs sufficient time for the forward and reverse reactions to establish equilibrium. The rate at which equilibrium is reached depends on the reaction kinetics and the complexity of the reaction.

When a system reaches dynamic equilibrium, the concentrations of reactants and products no longer change, but the reactions continue to occur. At equilibrium, the forward and reverse reactions are balanced, maintaining a constant ratio between the concentrations of reactants and products.