Limiting Reagents and Percent Yield

Limiting Reagents  

Definition: In a chemical reaction involving two or more reactants, the limiting reagent (or limiting reactant) is the one that is used up first.  

- Once the limiting reagent is consumed, the reaction stops, even if other reactants remain.  

- The excess reagent (or excess reactant) is the substance left over after the reaction.  

Key Points:  

- Reactions proceed until one reactant is completely used.  

- The limiting reagent controls the extent of the reaction and determines the amount of product formed.  

- Excess reactants remain unused after the reaction.  

Percent Yield  

Definition: Percent yield measures the efficiency of a chemical reaction.  

- It is the ratio of actual yield to theoretical yield, expressed as a percentage.  

Formula:  

% Yield = Actual Yield / Theoretical Yield x 100

Actual Yield: The amount of product obtained experimentally.  

Theoretical Yield: The maximum possible amount of product predicted by stoichiometric calculations.  

Example  

If a reaction is expected to produce 10 g of product (theoretical yield), but only 8 g is obtained experimentally (actual yield):  

% Yield = 8/10 x 100 = 80%