Question

How do you know if a problem is a limiting reactant problem?

Answer 1

For solving the limiting reactant problem, the chemical reaction should be balanced so that the mole ratio can be obtained. The limiting reactant is the reactant present in chemical reaction which fully gets consumed to form the product.

Complete step by step answer:
The limiting reactant is considered as the reactant which gets completely used up during the chemical reaction. The reactant is also known as limiting reagent or limiting agent. The limiting reactant is always present in lesser quantity.
The excess reactant is considered as the reactant which remains in the chemical reaction even after the reaction is complete. The excess reactant is also known as excess reagent or excess agent. The excess reactant is always present in higher quantities.
The limiting reactant can be determined by using two methods.
(1) Using the mole ratio
(2) Using the product approach

Example: Consider a reaction taking place between the hydrogen and oxygen to form water.
${H_2} + {O_2} \to {H_2}O$
Balance the equation
$2{H_2} + {O_2} \to 2{H_2}O$
As in the given reaction, hydrogen is used up twice as fast as the oxygen to form water, therefore the hydrogen will be limiting reagent and oxygen is the excess reagent.
When in a question, two reactants are given, first balance the whole chemical equation and check the amount of reactant B needed to react with A. If the amount of B obtained is greater than it is excess reagent and the reactant A is the limiting reagent.

Note:
You must know that while solving a limiting reagent question, the limiting reagent depends on the mole ratio and not on the masses of the reactants present in the chemical reaction.