Mole to Gram Stoichiometry (Mole to Mass) - Detailed Examples and ... - Free Printable

Let’s solve each example step by step, just like you would on your homework. We’ll use the balanced chemical equation:

N₂ + 3 H₂ → 2 NH₃

This tells us:
- 1 mole of N₂ reacts with 3 moles of H₂ to make 2 moles of NH₃.
- We can use this ratio to convert between moles of one substance and moles (or grams) of another.

We also need molar masses:
- N₂ = 2 × 14.01 = 28.02 g/mol (we’ll use 28.01 as in the worksheet)
- H₂ = 2 × 1.008 = 2.016 g/mol (not needed directly here)
- NH₃ = 14.01 + 3×1.008 = 17.034 g/mol (worksheet uses 17.04)

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Ex. 1: Given 2.5 moles of N₂, how many grams of NH₃ would be produced?

Step 1: Use mole ratio from equation — 1 mol N₂ makes 2 mol NH₃
→ So, 2.5 mol N₂ × (2 mol NH₃ / 1 mol N₂) = 5.0 mol NH₃

Step 2: Convert moles of NH₃ to grams
→ 5.0 mol NH₃ × 17.04 g/mol = 85.2 grams NH₃

✔ Matches worksheet answer.

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Ex. 2: Given 4.5 moles of H₂, how many grams of N₂ will be used?

Step 1: Mole ratio — 3 mol H₂ react with 1 mol N₂
→ So, 4.5 mol H₂ × (1 mol N₂ / 3 mol H₂) = 1.5 mol N₂

Step 2: Convert moles of N₂ to grams
→ 1.5 mol N₂ × 28.01 g/mol = 42.015 grams → rounds to 42.02 grams

✔ Matches worksheet answer.

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Ex. 3: Given 12.3 grams of NH₃, how many moles of N₂ were needed?

Step 1: Convert grams of NH₃ to moles
→ 12.3 g NH₃ ÷ 17.04 g/mol = 0.7218 mol NH₃

Step 2: Use mole ratio — 2 mol NH₃ come from 1 mol N₂
→ So, 0.7218 mol NH₃ × (1 mol N₂ / 2 mol NH₃) = 0.3609 mol N₂ → rounds to 0.36 mol

✔ Matches worksheet answer.

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Ex. 4: Given 56 grams of N₂, how many moles of NH₃ were produced?

Step 1: Convert grams of N₂ to moles
→ 56 g N₂ ÷ 28.01 g/mol = 1.999 mol N₂ ≈ 2.00 mol N₂

Step 2: Use mole ratio — 1 mol N₂ makes 2 mol NH₃
→ 2.00 mol N₂ × (2 mol NH₃ / 1 mol N₂) = 4.00 mol NH₃

✔ Matches worksheet answer.

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Final Answer:
All four examples are solved correctly using stoichiometry steps:
1. Convert given amount to moles (if needed).
2. Use mole ratio from balanced equation.
3. Convert to desired unit (grams or moles).

Answers:
Ex. 1: 85.2 grams NH₃
Ex. 2: 42.02 grams N₂
Ex. 3: 0.36 moles N₂
Ex. 4: 4.00 moles NH₃