Limiting Reagent and Percent Yield Chemistry Limiting Reagent and Percent Yield

Limiting and Excess Reagents An insufficient quantity of any of the reactants will limit the amount of product that forms. Limiting reagent – the reagent that determines the amount of product that can be formed. Excess reagent – the reagent that is not completely used up.

Determining the Limiting Reagent For the equation 2Cu(s) + S(s) → Cu2S(s) What is the limiting reagent when 80.0g Cu reacts with 25.0g S? Knowns: Cu = 80g S = 25.0g

80. 0g Cu x g Cu2S = 100 g Cu2S 128g Cu 160 g Cu2S 25 80.0g Cu x g Cu2S = 100 g Cu2S 128g Cu 160 g Cu2S 25.0g S x g Cu2S = 125 g Cu2S 32 g S 160 g Cu2S With the amounts you have, you can make more Cu2S with the sulfur, so Cu is the limiting reagent.

Using Limiting Reagent to Find Quantity of a Product For 2Cu(s) + S(s) → Cu2S(s) What is the maximum number of grams of Cu2S that can be formed when 80.0 g Cu reacts with 25.0g S? Previously determined that Cu is the limiting reagent. Solve for g Cu2S using only the Cu information.

Percent Yield Theoretical yield – the maximum amount of product that will form during a reaction. Actual yield – the amount of product that actually forms. Percent yield – ratio of actual to theoretical yield. Percent yield = actual yield X 100 theoretical yield

Calculating Theoretical Yield For CaCO2(s) → CaO(s) + CO2(g) What is the theoretical yield of CaO if 24.8g CaCO2 is heated? Knowns: CaCO2 = 100.1 g/mol CaO = 56.1 g/mol 24.8 g CaCO2 x g CaO = 13.9g CaO 100.1g CaCO2 56.1 g CaO

Calculating Percent Yield of a Reaction What is the percent yield if 13.1g CaO is actually produced when 24.8g CaCo3 is heated? Knowns: actual yield =13.1g CaO theoretical yield = 13.9g CaO 13.1g CaO X 100 = 94.2% 13.8g CaO

Homework - Worksheet