What is Limiting reactant?
In any chemical reaction, the limiting reactant(or reagent) is a substance which is fully absorbed when the chemical reaction is complete. This reagent limits the amount of the product generated and the reaction cannot continue without it. During the precipitation reaction, information about the limiting agent can be determined by the presence of incomplete precipitation. In dissolution reaction limiting reactant can be produced by the clear saturated or unsaturated solution. In the gaseous reaction by measuring the mixture of gases that are formed can identify the limiting reagent.
The procedure to determine the limiting reagent is as follows
- If the chemical formula is not balanced, balance it.
- Find the total number of moles of all the reactants during the reaction.
- During the reaction find out the total number of products are formed.
- Determine the reactant which gives less quantity of products, and that is called a limiting agent.
Example 1
2.3 g of sodium metal is transferred to a 3L flask filled with chlorine gas. Determine the limiting reagent and amount of excess reagent present if the mass of Na = 23 and Cl = 35.5.
Solution
The Balanced equation is
2.3 g of sodium metal = 2.3 / 23 = 0.1 mole
It requires 1 x 0.1/2 = 0.05 moles of chlorine
1 mole of chlorine gas = 22.4 L at STP
Therefore, 3 L = 3/22.4 = 0.1339 moles
Hence, Sodium metal is the limiting reactant.
The amount of Cl2 in excess is 0.1339 – 0.05 moles
= 0.0839 moles occupy 0.0839 x 22.4 / 1
= 1.88 L approximately.
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