Limiting Reactants and Percent Yield

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%