Q.Briefly explain the following:

(a) Reversible reactions proceed in both directions and reach equilibrium; irreversible reactions go essentially to completion in one direction. (b) At equilibrium, forward and reverse reactions continue at equal rates — equilibrium is dynamic, not static.

(a) Reversible and Irreversible reactions:

A reversible reaction is one that can proceed in both the forward and the backward direction simultaneously under the given conditions — the products can react with each other to regenerate the original reactants. Such reactions never go to 100% completion; instead, they reach a state of chemical equilibrium where both reactants and products are present together, with concentrations that no longer change with time. Reversible reactions are denoted with a double-headed arrow (⇌), e.g. N2(g) + 3H2(g) ⇌ 2NH3(g).

An irreversible reaction, by contrast, proceeds essentially only in the forward direction, converting reactants almost completely into products, with negligible reverse reaction under ordinary conditions. This often happens when a product escapes the system (e.g. as a gas or precipitate) or when the reaction is highly exothermic/has a very large equilibrium constant. Example: AgNO3(aq) + NaCl(aq) → AgCl(s)↓ + NaNO3(aq), or combustion reactions.

(b) Dynamic nature of chemical equilibrium:

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