Stoichiometry Loose Ends: Limiting Reactants, Percentage Yield, and Percentage Error

What is a limiting reactant? The substance that controls the quantity of products that can form in a chemical reaction. The substance that controls the quantity of products that can form in a chemical reaction. In other words, the reactant that limits the reaction because you run out of it. In other words, the reactant that limits the reaction because you run out of it. Every other reactant is called the excess reactants. Every other reactant is called the excess reactants.

How can we determine what is going to be the limiting reactant? Convert all reactants into the same product with the same substance unit. Convert all reactants into the same product with the same substance unit. The one that produces less product is the limiting reactant. The one that produces less product is the limiting reactant. So, it is the same as before, but you do it more than once. So, it is the same as before, but you do it more than once.

Percentage Yield The ratio of the experimental yield to the theoretical yield The ratio of the experimental yield to the theoretical yield Theoretical yield – book value, “correct answer,” the calculated value, value you were aiming at. Theoretical yield – book value, “correct answer,” the calculated value, value you were aiming at. Experimental yield – measured value, experimental value, value you got in the lab Experimental yield – measured value, experimental value, value you got in the lab

Formula Divide the experimental value by the theoretical yield and multiply by 100. Divide the experimental value by the theoretical yield and multiply by 100. Experimental yield Theoretical yield X 100

Percentage Error The margin of error expressed as a percent. The margin of error expressed as a percent. Formula Formula –Take the theoretical yield and subtract the experimental value. –Divide this value by the theoretical yield and multiply by 100% Theoretical yield - Experimental yield Theoretical yield X 100