1. Unit: Stoichiometry Excess Reactant Calculations Day 5 - Notes
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2. After today you will be able to…
Calculate the limiting reactant using other mole relationships
Calculate how much of the excess reactant reacts and how much is left over

3. Other L.R. Calculations
Example: How many moles of iron (III) oxide can be produced from the reaction of moles of iron with moles of oxygen? Word equation: Formula Equation:
Fe O-2
iron + oxygen  iron (III) oxide 4 Fe + 3 O2  2
Fe2O3
K: molFe
U: ? molFe2O3
Can be produced:
13.17 mol Fe 1
2 mol Fe2O3
4 mol Fe x
6.585 mol Fe2O3 =
K: molO2
U: ? molFe2O3
18.19 mol O2 1
2 mol Fe2O3
3 mol O2 x =
12.13 mol Fe2O3

4. Example: Limiting Reactant AND Excess Reactant Calculations
What mass of CoCl3 is formed from the reaction of 3.478x1023 atoms Co with 57.92L of Cl2 gas at STP?
How much of the excess reactant reacts and how much is left over?
2Co + 3Cl2  2CoCl3
1Co=58.78
3Cl=106.35
K: 3.478x1023 atomsCo
165.13g
U: ? gCoCl3 LR
3.478x1023atomsCo 1
1 mol Co
6.02x1023atomsCo
2 mol CoCl3
2 mol Co
165.13gCoCl3
1 mol CoCl3 x x x =
K: LCl2
U: ? gCoCl3
Can be produced:
95.40gCoCl3 ER
57.92L Cl2 1
1 mol Cl2
22.4L Cl2
2 mol CoCl3
3 mol Cl2 x
165.13gCoCl3
1 mol CoCl3 x x =
284.7gCoCl3

5. Example: Limiting Reactant AND Excess Reactant Calculations
What mass of CoCl3 is formed from the reaction of 3.478x1023 atoms Co with 57.92L of Cl2 gas at STP?
How much of the excess reactant reacts and how much is left over?
2Co + 3Cl2  2CoCl3
To find out how much excess reactant reacts, do a third calculation using the limiting reactant as the known, and the excess reactant as the unknown. LR ER
K: 3.478x1023atomsCo
U: ? L Cl2
3.478x1023atomsCo 1
1 mol Co
6.02x1023atomsCo
3 mol Cl2
2 mol Co
22.4L Cl2
1 mol Cl2 x x x =
Reacts:
19.41L Cl2

6. Example: Limiting Reactant AND Excess Reactant Calculations
What mass of CoCl3 is formed from the reaction of 3.478x1023 atoms Co with 57.92L of Cl2 gas at STP?
How much of the excess reactant reacts and how much is left over?
2Co + 3Cl2  2CoCl3
To find out how much is left over (unreacted), subtract the amount of the excess reactant that reacted from the original amount of excess reactant (from the problem). LR ER
57.92L Cl2
-19.41L Cl2
Left over:
38.51L Cl2

7. Questions?
Begin WS5
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