Question

Define limiting reactant give examples of limiting reactant reactant in chemical equations

Answer 1

The reactant that determines how much of the products are made, is known as limiting reagent The other reactants are referred to as being in excess reagent.

For example

If 120 mg Benzaldehyde reacts with 0.56 ml of 3M CH₃MgBr and produces 1-phenylethanol, Benzaldehyde is a limiting reagent and it determines how much 1-phenylethanol will be made.

To know, which reactant is a limiting reagent, calculate the moles of reactant. The reactant with least moles is a limiting reagent.

Write the reaction equation

PhCHO + CH₃MgBr --------> PhCHOHCH₃ + Mg²⁺ + Br^-

Given- PhCHO = 120 mg

CH₃MgBr = 0.56 ml

Step1: Calculate moles of Benzaldehyde

Mass of Benzaldehyde = 120 mg = 0.12 g

Molar mass of Benzaldehyde = 106.121 g/mol

Moles of Benzaldehyde = 0.12 g/106.121 g/mol = 0.00113 moles

Step2: Calculate moles of CH₃MgBr

Volume of CH₃MgBr = 0.56 ml

Molarity of CH₃MgBr = 3M

Moles of CH₃MgBr = C x V (L)

     = 3 x (0.56/1000) = 0.00168 moles

Moles of benzaldehyde are less than moles of CH₃MgBr, so benzaldehyde is limiting reagent.