3.3 Limiting and Non-Limiting Reactants

A limiting reactant is the reactant that is completely consumed in a reaction. A limiting reactant can also be defined as the reactant that produces the lowest moles of products in a reaction. The reactant in excess is the reactant left unutilised or unreacted after the reaction is complete. It is also referred to as a Non- Limiting reactant.

3.3.1 Identification of a Limiting Reactant in a Reaction

A limiting reactant can be recognised by calculating the number of moles of products formed from data of the given amounts of the reactants, using a balanced chemical equation. The reactant, that produces the least number of moles of products, is the limiting reactant. For example, 10 moles of ${\mathrm{H}}_2$$\mathrm{H}_{2}$ and 10 moles of ${\mathrm{O}}_2$$\mathrm{O}_{2}$ were reacted to produce ${\mathrm{H}}_2\mathrm{O}$$\mathrm{H}_{2}\mathrm{O}$ . Which one of the reactants is the limiting reactant? We can calculate as follows:

The reaction is $2{\mathrm{H}}_2(\mathrm{g})+{\mathrm{O}}_2(\mathrm{g})⟶2{\mathrm{H}}_2{\mathrm{O}}_{(\mathrm{g})}$$\mathrm{2H_{2}(g)} + \mathrm{O_{2}(g)}\longrightarrow \mathrm{2H_{2}O_{(g)}}$ According to the balanced chemical equation

2 moles of ${\mathrm{H}}_2$$\mathrm{H}_{2}$ give $=$ 2 moles of ${\mathrm{H}}_2\mathrm{O}$$\mathrm{H}_{2}\mathrm{O}$

10 moles of ${\mathrm{H}}_2$$\mathrm{H}_{2}$ will give $=$ $\frac{2}{2}\times 10=10$$\frac{2}{2}\times 10 = 10$ moles of ${\mathrm{H}}_2\mathrm{O}$$\mathrm{H}_{2}\mathrm{O}$