Worksheet teaching the principles of balancing chemical equations, emphasizing that atoms are neither created nor destroyed, and providing practice problems.

Let’s go step by step to balance each chemical equation. Remember: we can only add coefficients (numbers in front of formulas), never change subscripts!

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1. Mg + O₂ → MgO

Step 1: Count atoms on each side

Left:
Mg = 1
O = 2

Right:
Mg = 1
O = 1

→ Oxygen is not balanced.

Step 2: Fix oxygen

We have 2 O on left, 1 O on right → put a 2 in front of MgO:

Mg + O₂ → 2MgO

Now right side:
Mg = 2
O = 2

Left side:
Mg = 1
O = 2

→ Now magnesium is unbalanced.

Step 3: Fix magnesium

Put a 2 in front of Mg on left:

2Mg + O₂ → 2MgO

Check:

Left: Mg=2, O=2
Right: Mg=2, O=2 ✔ Balanced!

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2. Ca + O₂ → CaO

Left:
Ca = 1
O = 2

Right:
Ca = 1
O = 1

→ Oxygen unbalanced.

Put 2 in front of CaO:

Ca + O₂ → 2CaO

Right: Ca=2, O=2
Left: Ca=1, O=2 → Calcium now unbalanced.

Put 2 in front of Ca:

2Ca + O₂ → 2CaO

Check:

Left: Ca=2, O=2
Right: Ca=2, O=2 ✔ Balanced!

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3. N₂ + H₂ → NH₃

Left:
N = 2
H = 2

Right:
N = 1
H = 3

→ Both elements unbalanced.

Start with nitrogen: Put 2 in front of NH₃:

N₂ + H₂ → 2NH₃

Right: N=2, H=6
Left: N=2, H=2 → Hydrogen unbalanced.

Need 6 H on left → H₂ has 2 H per molecule → need 3 H₂:

N₂ + 3H₂ → 2NH₃

Check:

Left: N=2, H=6
Right: N=2, H=6 ✔ Balanced!

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4. Cu₂O + C → Cu + CO₂

Left:
Cu = 2
O = 1
C = 1

Right:
Cu = 1
O = 2
C = 1

→ Copper and oxygen unbalanced.

First, fix copper: Put 2 in front of Cu on right:

Cu₂O + C → 2Cu + CO₂

Now:
Left: Cu=2, O=1, C=1
Right: Cu=2, O=2, C=1 → Oxygen unbalanced.

Left has 1 O, right has 2 O → Need 2 O on left → Put 2 in front of Cu₂O:

2Cu₂O + C → 2Cu + CO₂

Wait — now left: Cu=4, O=2, C=1
Right: Cu=2, O=2, C=1 → Copper still unbalanced.

Fix copper again: Put 4 in front of Cu on right:

2Cu₂O + C → 4Cu + CO₂

Now check:

Left: Cu=4, O=2, C=1
Right: Cu=4, O=2, C=1 ✔ Balanced!

But wait — let’s double-check the carbon and oxygen.

CO₂ has 1 C and 2 O → matches left side (C=1, O=2 from 2Cu₂O). Yes!

Actually, this works:

2Cu₂O + 1C → 4Cu + 1CO₂

✔ All atoms match.

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5. H₂O₂ → H₂O + O₂

Left:
H = 2
O = 2

Right:
H = 2 (from H₂O)
O = 1 (from H₂O) + 2 (from O₂) = 3 → Unbalanced!

Try putting 2 in front of H₂O₂:

2H₂O₂ → H₂O + O₂

Left: H=4, O=4
Right: H=2, O=1+2=3 → Still bad.

Try putting 2 in front of H₂O:

2H₂O₂ → 2H₂O + O₂

Left: H=4, O=4
Right: H=4 (from 2H₂O), O=2 (from 2H₂O) + 2 (from O₂) = 4 ✔

Perfect!

So: 2H₂O₂ → 2H₂O + 1O₂

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## Final Answers:

Balanced equations with coefficients:

1. 2Mg + 1O₂ → 2MgO
Mg = 2, O = 2 on both sides

2. 2Ca + 1O₂ → 2CaO
Ca = 2, O = 2 on both sides

3. 1N₂ + 3H₂ → 2NH₃
N = 2, H = 6 on both sides

4. 2Cu₂O + 1C → 4Cu + 1CO₂
Cu = 4, O = 2, C = 1 on both sides

5. 2H₂O₂ → 2H₂O + 1O₂
H = 4, O = 4 on both sides

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Final Answer:
1. 2Mg + O₂ → 2MgO
2. 2Ca + O₂ → 2CaO
3. N₂ + 3H₂ → 2NH₃
4. 2Cu₂O + C → 4Cu + CO₂
5. 2H₂O₂ → 2H₂O + O₂