Limiting and Excess Reagents

You need 2 pieces of bread, 1 tablespoon of peanut butter and 2 tablespoons of jelly to make a sandwich.  If you have 10 pieces of bread, 4 tablespoons of peanut butter and 20 tablespoons of jelly, what is the limiting reactant?

• bread
• jelly
• peanut butter
• sandwich

Identify the limiting reagent when 6.00 moles HCl combines with 5.00 moles Mg to form MgCl₂.
 
1 Mg +  2 HCl --> 1 MgCl₂  +  1 H₂   
 

• Mg
• H₂
• MgCl₂
• HCl

The limiting reactant . . .

• slows the reaction down.
• is used up first.
• is the reactant that is left over.
• controls the speed of the reaction.

Use the equation 2 Al + 3 Cl₂ ---> 2 AlCl₃.  If 2 moles of aluminum and 2 moles of chlorine are reacted, identify the limiting reactant.

• AlCl₃
• Cl₂
• Al
• None

When does a chemical reaction stop?

• When the lab is finished.
• When the excess reactant is used. up
• When the limiting reactant is used up.
• Chemical reactions never stop.

When 12 moles of O₂ reacts with 6 moles of C₁₀H₈, what is the limiting reactant?  
1 C₁₀H₈ + 12 O₂ --> 10 CO₂ + 4 H₂O

• Oxygen
• C₁₀H₈
• Water
• Carbon Dioxide

4. If the quantities of reactants are given in units other than moles, what is the first step for determining the amount of product?

• Determine the amount of product from the given amount of limiting reagent.
• Convert each given quantity of reactant to moles.
• Identify the limiting reagent.

Identify the limiting reagent when 6.00 g HCl combines with 5.00 g Mg to form MgCl₂.

Mg + 2HCl --> MgCl₂ + H₂

• Mg

• H₂

• MgCl₂

• HCl

A reaction was predicted to produce 32.4 grams of a compound. When the product was measured, there were only 26.1 grams made. What is the percent yield?

• 80.6%
• 6.3%
• 24.1%
• 58.5%