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Limiting Reactants

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.

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Limiting Reactants

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  1. Limiting Reactants Which ingredient defines what I can make?

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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)

  7. % 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!

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