Limiting Reactants
In chemistry, a limiting reactant is the ingredient that restricts the amount of product we can produce. For example, when making cookies, if you have more sugar and eggs than Nutella, Nutella becomes the limiting reactant, capping your yield to a certain amount of cookies. The concept also applies in various scenarios, like car production. By identifying limiting reactants, such as magnesium in a reaction to produce magnesium oxide, we can calculate the theoretical yield and even percent yield to evaluate reaction efficiency.
Limiting Reactants
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Presentation Transcript
Limiting Reactants Which ingredient defines what I can make?
What’s a limiting reactant? • A limiting reactant is the reactant that limits what you can produce. Duh! • In other words, it’s the reactant that would produce less of the product.
Examples • For example, suppose I have my Nutella cookie recipe (1 cup Nutella, 1 cup sugar, and 1 egg make 30 cookies). • And suppose I have 3 cups of Nutella, 5 cups of sugar, and 12 eggs • 3 cups Nutellax 30 cookies = 90 cookies 1 cup Nutella • 5 cups sugar x 30 cookies = 150 cookies 1 cup sugar • 12 eggs x 30 cookies = 360 cookies 1 egg • The 3 cups of Nutella produces the least number of cookies (product), so Nutella is the limiting reactant.
Example • Suppose you own a car factory, the “recipe” for cars is 1 car body and 4 wheels makes 1 car. You have 36 wheels and 10 car bodies. • 36 wheels x 1 car = 9 cars 4 wheels • 10 car bodies x 1 car = 10 cars 1 car body • The 36 wheels can only make 9 cars, so the wheels are the limiting factor.
Example Calculate the mass of Magnesium oxide produced if you have 2.40 g Mg and 10.0 g O2 (2Mg + O2 2MgO) • 2.40 g Mg x 1 mol Mg x 2 molMgO x 40.3 g MgO= 3.98 g MgO 1 24.3 g Mg 2 mol Mg 1 molMgO • 10.0 g O2 x 1 mol O2 x 2 molMgO x 40.3 g MgO = 25.2 g MgO 1 32.0 g O2 1 mol O2 1 molMgO • The magnesium limits the reaction to producing only 3.98 g of magnesium oxide. • Magnesium is the limiting reactant. • The reaction (theoretically) produces 3.98 g magnesium oxide
Which Brings us to… • Percent Yield or, did I get what I should have gotten? • Percent yield measures how close you got to what you should have produced. • The formula for percent yield is: % yield = Actual yield (when you carried out the reaction) x 100 Theoretical yield (From the stoichiometry)
% Yield Example • So let’s say we carried out the reaction from before with 2.40 g of magnesium producing theoretically) 3.98 g of magnesium oxide. • And suppose that, when we carried out the reaction, we were able to produce 3.45 g of magnesium oxide. • What is our percent yield? Actual yield (3.45 g) x 100 = 86.7% yield Theoretical (3.98 g) Not baaaad!
