Limiting & Excess

Cookie Stoichiometry• To make one batch,

it requires:• 2 eggs• 2 cups of flour• 2/3 cups of butter

• How many batches could you make with…– 4 eggs– 6 cups of flour– 2/3 cups of butter

– The cups of butter was your limiting reagent– The eggs and flour were your excess reagents– But how could you show this

mathematically…?

2 Together…. 3 on your Own!Whiteboard!

Example 1

20.00 g of H2 react with 100.0 g of O2 according to the reaction

2 H2 + O2 2 H2O

Which reactant is limiting and which reactant is in excess?

Example 11. Calculate the number of moles of a product formed.

Mole of H2O (based on

H2)= 20.00 g

H2x

1 mol H2

x

2 mol H2O

= 10.0 mole H2O

2.0 g H2 2 mol H2

Mole of H2O (based on O2)

= 100.0 g O2 x1 mol O2

x2 mol H2O

=6.25 mol H2O

32.0 g O2 1 mol O2

Example 1

Determine the limiting and excess reactants.

O2 is the limiting reactant.

H2 is the excess reactant.

2. How much H2 (in grams) is left after O2 runs out?

Example 1

3. To find mass of H2 in excess, find the mass of H2 which will react based on the mass of the limiting reactant.Mass of H2

(based on O2)= 100.0 g O2 x

1 mol O2 x2 mol H2 x

2.0 g H2 = 12.5 g H232.0 g O2 1 mol O2 1 mol H2

Example 1

4. Then, subtract the mass of H2 which reacts from the starting mass of H2.

Mass of H2 (in excess)

= mass H2 (at start) – mass H2 (reacted)

= 20.00 g – 12.5g = 7.5 g

Take Attendance

Example 2

If 56.8 g of FeCl2, 14.9 g of KNO3 and 40.0 g of HCl are mixed according to the reaction

FeCl2 + KNO3 + HCl FeCl3 + NO + H2O + KCl

a) What is the limiting reactant?

b) How many grams of each “excess” reactant left in the reaction vessel?

Example 2

If 56.8 g of FeCl2, 14.9 g of KNO3 and 40.0 g of HCl are mixed according to the reaction

3 FeCl2 + KNO3 + 4 HCl 3 FeCl3 + NO + 2 H2O + KCl

a) What is the limiting reactant?

b) How many grams of each “excess” reactant left in the reaction vessel?

Example 2If 56.8 g of FeCl2, 14.9 g of KNO3 and 40.0 g of HCl are mixed according to the reaction

3 FeCl2 + KNO3 + 4 HCl 3 FeCl3 + NO + 2 H2O + KCl

a) What is the limiting reactant? KNO3

b) How many grams of each “excess” reactant left in the reaction vessel?

Example 2If 56.8 g of FeCl2, 14.9 g of KNO3 and 40.0 g of HCl are mixed according to the reaction

3 FeCl2 + KNO3 + 4 HCl 3 FeCl3 + NO + 2 H2O + KCl

a) What is the limiting reactant? KNO3

b) b) How many grams of each “excess” reactant are actually present in excess? FeCl2 = 0.8g, HCl = 18.5g

Example 3If 3.2 g of CuSO4, 2.5 g of water and 3.0 g of SO2 are reacted together in the reaction:

CuSO4 + H2O + SO2 Cu + H2SO4• Which reactant is the limiting reactant?• What is the mass of each of the excess reactants?

Example 4700. mL of 0.350 M ammonia (NH3) solution is mixed with 15.0 g of solid magnesium to produce magnesium nitride and hydrogen gas.• Which reactant is in excess?• How much (in grams) of the excess reactant

remains after the reaction is complete?

Example 5:For the reaction:

TiO2(aq) + B4C(g) + C(s) TiB2(aq) + CO(g)

If 11.5 L of 0.800 M TiO2, 455 g of solid carbon and 184 L of B4C gas at STP react together. Find the amount (based on the original units given) of the reactants left over.

Example 5:For the reaction:

2TiO2(aq) + B4C(g) + 3 C(s) 2TiB2(aq) + 4CO(g)

If 11.5 L of 0.800 M TiO2, 455 g of solid carbon and 184 L of B4C gas at STP react together. Find the amount (based on the original units given) of the reactants left over.