Limiting Reactants and Percent Yield

Mr. Anderson explains the concept of limiting reactants and percent yield in chemical reactions. He uses a cookie recipe analogy to introduce limiting reactants, followed by examples of hydrogen and methane combustion to illustrate the concept. The video also covers the calculation of limiting reactants using moles and explains how to determine percent yield, emphasizing the difference between predicted and actual yields in reactions.

What is a limiting reactant in a chemical reaction?

• The reactant that is completely used up first

• The catalyst used in the reaction

• The reactant that is in excess

• The product formed in the reaction

In the analogy of making cookies, what happens if you have only one egg but need two?

• You cannot make any cookies

• You make twice as many cookies

• You make cookies without eggs

• You make half the amount of cookies

In the hydrogen combustion example, what was the limiting reactant?

• Carbon dioxide

• Water

• Hydrogen gas

• Oxygen gas

What is left over in the methane combustion example when methane is the limiting reactant?

• Carbon dioxide

• Methane

• Water

• Oxygen

Why can't you determine the limiting reactant by just looking at the mass of reactants?

• Because mass is irrelevant in chemical reactions

• Because mass is not measurable

• Because mass does not account for molecular weight

• Because mass is always the same for all reactants

What is the first step in calculating the limiting reactant?

• Convert grams to moles

• Identify the products

• Convert moles to grams

• Calculate the percent yield

In the example calculation, which reactant was the limiting reactant?

• Methane

• Carbon dioxide

• Oxygen

• Water

What does percent yield compare?

• Theoretical yield to actual yield

• Reactant mass to product mass

• Reactant volume to product volume

• Theoretical yield to reactant mass

Why is the percent yield never 100%?

• Because not all molecules react perfectly

• Because some reactants are always left over

• Because the reaction is always incomplete

• Because the products are always impure

If the actual yield is 6.19 grams and the predicted yield is 6.88 grams, what is the percent yield?

• 85.0%

• 95.0%

• 100.0%

• 90.0%