Solving Limiting Solving Limiting Reactant ProblemsReactant Problems

BackgroundBackground

In In limiting reactant problemslimiting reactant problems, we have the , we have the amounts (masses or mols) of two of the amounts (masses or mols) of two of the reactants.reactants.

The problem is always to find out which one of The problem is always to find out which one of the reactants is “the reactants is “limitinglimiting.”.”

The The limiting reactantlimiting reactant is the one that we will is the one that we will run out of first.run out of first.

The other reactant will be in The other reactant will be in excessexcess and will and will not be totally used up in the reaction.not be totally used up in the reaction.

BackgroundBackground

We will be using the same techniques we use We will be using the same techniques we use to solve to solve idealideal stoichiometric problems. stoichiometric problems.

We will use We will use molar massesmolar masses and and mole ratiomole ratios s to determine the limiting reactant.to determine the limiting reactant.

We will also use these values to figure out We will also use these values to figure out how much product we can expect from that how much product we can expect from that limiting reactant.limiting reactant.

ExampleExample

How much carbon dioxide is produced in the How much carbon dioxide is produced in the combustion reaction of 155 g of pentane, combustion reaction of 155 g of pentane, CC55HH1212, with 350 g of oxygen gas, O, with 350 g of oxygen gas, O22??

CC55HH1212((ll) + 8O) + 8O22((gg) → 5CO) → 5CO22((gg) + 6H) + 6H22O(O(ll))

ExampleExample

How much carbon dioxide is produced in the How much carbon dioxide is produced in the combustion reaction of 155 g of pentane, combustion reaction of 155 g of pentane, CC55HH1212, with 350 g of oxygen gas, O, with 350 g of oxygen gas, O22??

CC55HH1212((ll) + 8O) + 8O22((gg) → 5CO) → 5CO22((gg) + 6H) + 6H22O(O(ll))

First, we list the molar masses of the compounds.First, we list the molar masses of the compounds.

ExampleExample

How much carbon dioxide is produced in the How much carbon dioxide is produced in the combustion reaction of 155 g of pentane, combustion reaction of 155 g of pentane, CC55HH1212, with 350 g of oxygen gas, O, with 350 g of oxygen gas, O22??

CC55HH1212((ll) + 8O) + 8O22((gg) → 5CO) → 5CO22((gg) + 6H) + 6H22O(O(ll))M (g/mol) 72.0 32.0 44.0 18.0M (g/mol) 72.0 32.0 44.0 18.0

First, we list the molar masses of the compounds.First, we list the molar masses of the compounds.

Next, put in our known values and our unknown Next, put in our known values and our unknown quantity.quantity.

ExampleExample

How much carbon dioxide is produced in the How much carbon dioxide is produced in the combustion reaction of 155 g of pentane, combustion reaction of 155 g of pentane, CC55HH1212, with 350 g of oxygen gas, O, with 350 g of oxygen gas, O22??

CC55HH1212((ll) + 8O) + 8O22((gg) → 5CO) → 5CO22((gg) + 6H) + 6H22O(O(ll))M (g/mol) 72.0 32.0 44.0 18.0M (g/mol) 72.0 32.0 44.0 18.0

Next, put in our known values and our unknown Next, put in our known values and our unknown quantity.quantity.

m (g) 155 350m (g) 155 350 ( ? )( ? )

ExampleExample

How much carbon dioxide is produced in the How much carbon dioxide is produced in the combustion reaction of 155 g of pentane, combustion reaction of 155 g of pentane, CC55HH1212, with 350 g of oxygen gas, O, with 350 g of oxygen gas, O22??

CC55HH1212((ll) + 8O) + 8O22((gg) → 5CO) → 5CO22((gg) + 6H) + 6H22O(O(ll))M (g/mol) 72.0 32.0 44.0 18.0M (g/mol) 72.0 32.0 44.0 18.0

Next, calculate the number of moles of the Next, calculate the number of moles of the knowns.knowns.

m (g) 155 350m (g) 155 350 ( ? )( ? )

ExampleExample

How much carbon dioxide is produced in the How much carbon dioxide is produced in the combustion reaction of 155 g of pentane, combustion reaction of 155 g of pentane, CC55HH1212, with 350 g of oxygen gas, O, with 350 g of oxygen gas, O22??

CC55HH1212((ll) + 8O) + 8O22((gg) → 5CO) → 5CO22((gg) + 6H) + 6H22O(O(ll))M (g/mol) 72.0 32.0 44.0 18.0M (g/mol) 72.0 32.0 44.0 18.0

Next, calculate the number of moles of the Next, calculate the number of moles of the knowns.knowns.

m (g) 155 350m (g) 155 350 ( ? )( ? )

ExampleExample

How much carbon dioxide is produced in the How much carbon dioxide is produced in the combustion reaction of 155 g of pentane, combustion reaction of 155 g of pentane, CC55HH1212, with 350 g of oxygen gas, O, with 350 g of oxygen gas, O22??

CC55HH1212((ll) + 8O) + 8O22((gg) → 5CO) → 5CO22((gg) + 6H) + 6H22O(O(ll))M (g/mol) 72.0 32.0 44.0 18.0M (g/mol) 72.0 32.0 44.0 18.0

n n (mol)(mol)

nnC5H12C5H12 = = = 2.15 = = = 2.15 molmol

mmC5H12C5H12 155 g 155 gMMC5H12C5H12 72.0 g/mol 72.0 g/mol

m (g) 155 350m (g) 155 350 ( ? )( ? )

ExampleExample

How much carbon dioxide is produced in the How much carbon dioxide is produced in the combustion reaction of 155 g of pentane, combustion reaction of 155 g of pentane, CC55HH1212, with 350 g of oxygen gas, O, with 350 g of oxygen gas, O22??

CC55HH1212((ll) + 8O) + 8O22((gg) → 5CO) → 5CO22((gg) + 6H) + 6H22O(O(ll))M (g/mol) 72.0 32.0 44.0 18.0M (g/mol) 72.0 32.0 44.0 18.0

n n (mol)(mol)

nnC5H12C5H12 = = = 2.15 = = = 2.15 molmol

mmC5H12C5H12 155 g 155 gMMC5H12C5H12 72.0 g/mol 72.0 g/mol

2.152.15m (g) 155 350m (g) 155 350 ( ? )( ? )

ExampleExample

How much carbon dioxide is produced in the How much carbon dioxide is produced in the combustion reaction of 155 g of pentane, combustion reaction of 155 g of pentane, CC55HH1212, with 350 g of oxygen gas, O, with 350 g of oxygen gas, O22??

CC55HH1212((ll) + 8O) + 8O22((gg) → 5CO) → 5CO22((gg) + 6H) + 6H22O(O(ll))M (g/mol) 72.0 32.0 44.0 18.0M (g/mol) 72.0 32.0 44.0 18.0

n n (mol)(mol)

nnO2O2 = = = 10.94 = = = 10.94 molmol

mmO2O2 350 g 350 gMMO2O2 32.0 g/mol 32.0 g/mol

m (g) 155 350m (g) 155 350 ( ? )( ? )

ExampleExample

How much carbon dioxide is produced in the How much carbon dioxide is produced in the combustion reaction of 155 g of pentane, combustion reaction of 155 g of pentane, CC55HH1212, with 350 g of oxygen gas, O, with 350 g of oxygen gas, O22??

CC55HH1212((ll) + 8O) + 8O22((gg) → 5CO) → 5CO22((gg) + 6H) + 6H22O(O(ll))M (g/mol) 72.0 32.0 44.0 18.0M (g/mol) 72.0 32.0 44.0 18.0

n n (mol)(mol)

2.152.15

nnO2O2 = = = 10.94 = = = 10.94 molmol

mmO2O2 350 g 350 gMMO2O2 32.0 g/mol 32.0 g/mol

10.9410.94m (g) 155 350m (g) 155 350 ( ? )( ? )

ExampleExample

How much carbon dioxide is produced in the How much carbon dioxide is produced in the combustion reaction of 155 g of pentane, combustion reaction of 155 g of pentane, CC55HH1212, with 350 g of oxygen gas, O, with 350 g of oxygen gas, O22??

CC55HH1212((ll) + 8O) + 8O22((gg) → 5CO) → 5CO22((gg) + 6H) + 6H22O(O(ll))M (g/mol) 72.0 32.0 44.0 18.0M (g/mol) 72.0 32.0 44.0 18.0

n n (mol)(mol)

2.152.15

If we used up all 2.15 mols of the CIf we used up all 2.15 mols of the C55HH1212, we would , we would need 8×2.15 mol = 17.20 mols of Oneed 8×2.15 mol = 17.20 mols of O22..

m (g) 155 350m (g) 155 350 ( ? )( ? )

ExampleExample

How much carbon dioxide is produced in the How much carbon dioxide is produced in the combustion reaction of 155 g of pentane, combustion reaction of 155 g of pentane, CC55HH1212, with 350 g of oxygen gas, O, with 350 g of oxygen gas, O22??

CC55HH1212((ll) + 8O) + 8O22((gg) → 5CO) → 5CO22((gg) + 6H) + 6H22O(O(ll))M (g/mol) 72.0 32.0 44.0 18.0M (g/mol) 72.0 32.0 44.0 18.0

n n (mol)(mol)

2.152.15 10.9410.94

We only have 10.94 mols of OWe only have 10.94 mols of O22. Therefore, O. Therefore, O22 is is the limiting reactant.the limiting reactant.

m (g) 155 350m (g) 155 350 ( ? )( ? )

ExampleExample

How much carbon dioxide is produced in the How much carbon dioxide is produced in the combustion reaction of 155 g of pentane, combustion reaction of 155 g of pentane, CC55HH1212, with 350 g of oxygen gas, O, with 350 g of oxygen gas, O22??

CC55HH1212((ll) + 8O) + 8O22((gg) → 5CO) → 5CO22((gg) + 6H) + 6H22O(O(ll))M (g/mol) 72.0 32.0 44.0 18.0M (g/mol) 72.0 32.0 44.0 18.0

n n (mol)(mol)

2.152.15 10.9410.94

Now, we can calculate the number of mols of CONow, we can calculate the number of mols of CO22 produced.produced.

m (g) 155 350m (g) 155 350 ( ? )( ? )

ExampleExample

How much carbon dioxide is produced in the How much carbon dioxide is produced in the combustion reaction of 155 g of pentane, combustion reaction of 155 g of pentane, CC55HH1212, with 350 g of oxygen gas, O, with 350 g of oxygen gas, O22??

CC55HH1212((ll) + 8O) + 8O22((gg) → 5CO) → 5CO22((gg) + 6H) + 6H22O(O(ll))M (g/mol) 72.0 32.0 44.0 18.0M (g/mol) 72.0 32.0 44.0 18.0

n n (mol)(mol)

2.152.15 10.9410.94

nnCO2CO2 = n = nO2O2 × = 10.94 mol × = × = 10.94 mol × = 6.84 mol6.84 mol

coefficient COcoefficient CO22 55 coefficient Ocoefficient O22 88

m (g) 155 350m (g) 155 350 ( ? )( ? )

ExampleExample

How much carbon dioxide is produced in the How much carbon dioxide is produced in the combustion reaction of 155 g of pentane, combustion reaction of 155 g of pentane, CC55HH1212, with 350 g of oxygen gas, O, with 350 g of oxygen gas, O22??

CC55HH1212((ll) + 8O) + 8O22((gg) → 5CO) → 5CO22((gg) + 6H) + 6H22O(O(ll))M (g/mol) 72.0 32.0 44.0 18.0M (g/mol) 72.0 32.0 44.0 18.0

n n (mol)(mol)

2.152.15 10.9410.94

nnCO2CO2 = n = nO2O2 × = 10.94 mol × = × = 10.94 mol × = 6.84 mol6.84 mol

coefficient COcoefficient CO22 55 coefficient Ocoefficient O22 88

6.846.84m (g) 155 350m (g) 155 350 ( ? )( ? )

ExampleExample

How much carbon dioxide is produced in the How much carbon dioxide is produced in the combustion reaction of 155 g of pentane, combustion reaction of 155 g of pentane, CC55HH1212, with 350 g of oxygen gas, O, with 350 g of oxygen gas, O22??

CC55HH1212((ll) + 8O) + 8O22((gg) → 5CO) → 5CO22((gg) + 6H) + 6H22O(O(ll))M (g/mol) 72.0 32.0 44.0 18.0M (g/mol) 72.0 32.0 44.0 18.0

n n (mol)(mol)

2.152.15 10.9410.94

Finally, we can calculate the amount of COFinally, we can calculate the amount of CO22 produced.produced.

m (g) 155 350m (g) 155 350 ( ? )( ? )

ExampleExample

How much carbon dioxide is produced in the How much carbon dioxide is produced in the combustion reaction of 155 g of pentane, combustion reaction of 155 g of pentane, CC55HH1212, with 350 g of oxygen gas, O, with 350 g of oxygen gas, O22??

CC55HH1212((ll) + 8O) + 8O22((gg) → 5CO) → 5CO22((gg) + 6H) + 6H22O(O(ll))M (g/mol) 72.0 32.0 44.0 18.0M (g/mol) 72.0 32.0 44.0 18.0

n n (mol)(mol)

2.152.15 10.9410.94 6.846.84

m (g) 155 350m (g) 155 350 ( ? )( ? )

mmCO2CO2 = n = nCO2CO2 × M × MCO2CO2 = (6.84 mol)(44.0 g/mol) = = (6.84 mol)(44.0 g/mol) = 301 g301 g

ExampleExample

How much carbon dioxide is produced in the How much carbon dioxide is produced in the combustion reaction of 155 g of pentane, combustion reaction of 155 g of pentane, CC55HH1212, with 350 g of oxygen gas, O, with 350 g of oxygen gas, O22??

CC55HH1212((ll) + 8O) + 8O22((gg) → 5CO) → 5CO22((gg) + 6H) + 6H22O(O(ll))M (g/mol) 72.0 32.0 44.0 18.0M (g/mol) 72.0 32.0 44.0 18.0

n n (mol)(mol)

2.152.15 10.9410.94 6.846.84

301301m (g) 155 350m (g) 155 350

mmCO2CO2 = n = nCO2CO2 × M × MCO2CO2 = (6.84 mol)(44.0 g/mol) = = (6.84 mol)(44.0 g/mol) = 301 g301 g

ExampleExample

How much carbon dioxide is produced in the How much carbon dioxide is produced in the combustion reaction of 155 g of pentane, combustion reaction of 155 g of pentane, CC55HH1212, with 350 g of oxygen gas, O, with 350 g of oxygen gas, O22??

CC55HH1212((ll) + 8O) + 8O22((gg) → 5CO) → 5CO22((gg) + 6H) + 6H22O(O(ll))M (g/mol) 72.0 32.0 44.0 18.0M (g/mol) 72.0 32.0 44.0 18.0

n n (mol)(mol)

2.152.15 10.9410.94 6.846.84

301301m (g) 155 350m (g) 155 350

mmCO2CO2 = n = nCO2CO2 × M × MCO2CO2 = (6.84 mol)(44.0 g/mol) = = (6.84 mol)(44.0 g/mol) = 301 g301 g

ExampleExample

How much carbon dioxide is produced in the How much carbon dioxide is produced in the combustion reaction of 155 g of pentane, combustion reaction of 155 g of pentane, CC55HH1212, with 350 g of oxygen gas, O, with 350 g of oxygen gas, O22??

CC55HH1212((ll) + 8O) + 8O22((gg) → 5CO) → 5CO22((gg) + 6H) + 6H22O(O(ll))M (g/mol) 72.0 32.0 44.0 18.0M (g/mol) 72.0 32.0 44.0 18.0

n n (mol)(mol)

2.152.15 10.9410.94 6.846.84