Stoichiometry worksheet and key featuring problems on mole conversions using balanced chemical equations.

Let’s solve each problem step by step using the balanced chemical equations and mole ratios.

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Problem 1: How many moles of O₂ will be formed from 1.65 moles of KClO₃?

Balanced equation:
2 KClO₃ → 2 KCl + 3 O₂

Mole ratio:
From the equation, 2 mol KClO₃ → 3 mol O₂

So we set up:

> 1.65 mol KClO₃ × (3 mol O₂ / 2 mol KClO₃) = ?

Calculate:
(1.65 × 3) ÷ 2 = 4.95 ÷ 2 = 2.475 mol O₂

✔ Final Answer for #1: 2.48 mol O₂ (rounded to 3 significant figures)

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Problem 2: How many moles of KClO₃ are needed to make 3.50 moles of KCl?

Same equation:
2 KClO₃ → 2 KCl + 3 O₂

Mole ratio:
2 mol KClO₃ → 2 mol KCl, so it’s a 1:1 ratio!

So:

> 3.50 mol KCl × (2 mol KClO₃ / 2 mol KCl) = 3.50 mol KClO₃

✔ Final Answer for #2: 3.50 mol KClO₃

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Problem 3: How many moles of KCl will be formed from 2.73 moles of KClO₃?

Equation:
2 KClO₃ → 2 KCl + 3 O₂

Ratio: 2 mol KClO₃ → 2 mol KCl → again 1:1

So:

> 2.73 mol KClO₃ × (2 mol KCl / 2 mol KClO₃) = 2.73 mol KCl

✔ Final Answer for #3: 2.73 mol KCl

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Problem 4: How many moles of Fe₂O₃ are produced when 0.275 moles of Fe is reacted?

Equation:
4 Fe + 3 O₂ → 2 Fe₂O₃

Ratio: 4 mol Fe → 2 mol Fe₂O₃

Set up:

> 0.275 mol Fe × (2 mol Fe₂O₃ / 4 mol Fe) = ?

Calculate:
(0.275 × 2) ÷ 4 = 0.55 ÷ 4 = 0.1375 mol Fe₂O₃

✔ Final Answer for #4: 0.138 mol Fe₂O₃ (rounded to 3 sig figs)

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Problem 5: How many moles of Fe₂O₃ are produced when 31.0 moles of O₂ is reacted?

Equation:
4 Fe + 3 O₂ → 2 Fe₂O₃

Ratio: 3 mol O₂ → 2 mol Fe₂O₃

Set up:

> 31.0 mol O₂ × (2 mol Fe₂O₃ / 3 mol O₂) = ?

Calculate:
(31.0 × 2) ÷ 3 = 62.0 ÷ 3 ≈ 20.666... mol Fe₂O₃

✔ Final Answer for #5: 20.7 mol Fe₂O₃ (rounded to 3 sig figs)

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Problem 6: How many moles of O₂ are needed to react with 8.9 moles of Fe?

Equation:
4 Fe + 3 O₂ → 2 Fe₂O₃

Ratio: 4 mol Fe → 3 mol O₂

Set up:

> 8.9 mol Fe × (3 mol O₂ / 4 mol Fe) = ?

Calculate:
(8.9 × 3) ÷ 4 = 26.7 ÷ 4 = 6.675 mol O₂

✔ Final Answer for #6: 6.7 mol O₂ (rounded to 2 sig figs — since 8.9 has 2)

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Problem 7: How many moles of O₂ are produced when 1.26 moles of H₂O is reacted?

Equation:
2 H₂O → 2 H₂ + O₂

Ratio: 2 mol H₂O → 1 mol O₂

Set up:

> 1.26 mol H₂O × (1 mol O₂ / 2 mol H₂O) = ?

Calculate:
1.26 ÷ 2 = 0.63 mol O₂

✔ Final Answer for #7: 0.630 mol O₂ (keep 3 sig figs)

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Problem 8: How many moles of H₂O are needed to produce 55.7 moles of H₂?

Equation:
2 H₂O → 2 H₂ + O₂

Ratio: 2 mol H₂O → 2 mol H₂ → 1:1

So:

> 55.7 mol H₂ × (2 mol H₂O / 2 mol H₂) = 55.7 mol H₂O

✔ Final Answer for #8: 55.7 mol H₂O

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Problem 9: If enough H₂O is reacted to produce 3.40 moles of H₂, then how many moles of O₂ must have been made?

Equation:
2 H₂O → 2 H₂ + O₂

Look at products:
For every 2 mol H₂ produced, you get 1 mol O₂

So ratio: 2 mol H₂ → 1 mol O₂

Set up:

> 3.40 mol H₂ × (1 mol O₂ / 2 mol H₂) = ?

Calculate:
3.40 ÷ 2 = 1.70 mol O₂

✔ Final Answer for #9: 1.70 mol O₂

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Final Answer:
1. 2.48 mol O₂
2. 3.50 mol KClO₃
3. 2.73 mol KCl
4. 0.138 mol Fe₂O₃
5. 20.7 mol Fe₂O₃
6. 6.7 mol O₂
7. 0.630 mol O₂
8. 55.7 mol H₂O
9. 1.70 mol O₂