Limiting and Excess Reactant

Limiting reactants and Percentage yield

Reactants

• Limiting reactant- reactant that limits the amount of the other reactant that can combine and the amount of product that can form in a chemical reaction

• Excess reactant- The substance that is not used up completely in a reaction

Example Limiting Reaction

• Silicon Dioxide(quartz) is usually quite unreactive but reacts readily with hydrogen fluoride according to the following equation.

• SiO₂(s) + 4HF (g) ---> SiF₄(g) + 2H₂)(l)

• If 6.0 mol HF is added to 4.5 mol SiO₂, which is the limiting reactant?

Multiple Choice

Some Rocket engines use a mixture of hydrazine, N₂H₄, and hydrogen peroxide, H₂O₂, as the propellant. The reaction is given by the following equation.

N₂H₄(l) + 2H₂O₂(l) ---> N₂(g) + 4H₂O(g)

What is the limiting reactant in this reaction when .750 mol N₂H₄ is mixed with .500 mol H₂O₂?

• H₂O₂

• N₂H₄

Multiple Choice

Some Rocket engines use a mixture of hydrazine, N₂H₄, and hydrogen peroxide, H₂O₂, as the propellant. The reaction is given by the following equation.

N₂H₄(l) + 2H₂O₂(l) ---> N₂(g) + 4H₂O(g)

What is the limiting reactant in this reaction when .750 mol N₂H₄ is mixed with .500 mol H₂O₂?

• H₂O₂

• N₂H₄

Multiple Select

Some Rocket engines use a mixture of hydrazine, N₂H₄, and hydrogen peroxide, H₂O₂, as the propellant. The reaction is given by the following equation.

N₂H₄(l) + 2H₂O₂(l) ---> N₂(g) + 4H₂O(g)

How much of each product in moles if formed?

• .250 mol N₂

• 1.00 mol H₂O

• .500 mol H₂O

• 1.mol N₂

Yield and Percentage Yield

• Theoretical yield- maximum amount of product that can be produced from a given amount of reactant

• Actual Yield- the measured amount of a product obtained from a reaction

• Percentage yield- the ratio of the actual yield to the theoretical yield, multiplied by 100

• percentage yield

   $\frac{actual\ yield}{theoretical\ yield}x\ 100$  

Percentage yield

• Chorobenzane, C₆H₅Cl, is used in the production of many important chemicals, such as aspirin, dyes, and disinfectants. ONe industrial method of preparing chlorobenzane is to react to benzene, C₆H₆, with chlorine, as represented by the following equation.

• C₆H₆(l) + Cl₂(g) ----> C₆H₅Cl(l) + HCl(g)

• When 36.8g C₆H₆ reacts with an excess of Cl₂, the actual yield of C₆H₅Cl is 38.8 g. What is the percentge yield of C₆H₅Cl?

Multiple Choice

Methanol can be produced through the reaction of CO and H₂ in the presence of a catalyst.

CO(g) + 2H₂(g) --catalyst--> CH₃OH(l)

If 75.0g of CO react to produce 68.4 g CH₃OH, what is the percentage yield of CH₃OH?

• 79.7%

• 75.3%

• 68.4%

• 72.9%