Balancing Act worksheet for learning how to balance chemical equations.

Let’s solve this step by step.

We are balancing chemical equations. That means we need the same number of each type of atom on both sides of the arrow (reactants and products).

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First equation: Mg + O₂ → MgO

Step 1: Count atoms on each side.

Left:
Mg = 1
O = 2 (because O₂ has two oxygen atoms)

Right:
Mg = 1
O = 1

Not balanced — oxygen is 2 on left, 1 on right.

Step 2: Pick an element that’s not equal — let’s pick oxygen.

To get 2 oxygens on the right, put a 2 in front of MgO:

→ Mg + O₂ → 2 MgO

Now check again:

Left:
Mg = 1
O = 2

Right:
Mg = 2 (because 2 × MgO)
O = 2

Now magnesium is unbalanced! Left has 1, right has 2.

So put a 2 in front of Mg on the left:

→ 2 Mg + O₂ → 2 MgO

Check:

Left:
Mg = 2
O = 2

Right:
Mg = 2
O = 2

✔ Balanced!

Final coefficients: 2, 1, 2

(We don’t write “1” usually, but for counting it’s fine.)

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Second equation: Ca + O₂ → CaO

Left:
Ca = 1
O = 2

Right:
Ca = 1
O = 1

Unbalanced oxygen.

Put 2 in front of CaO:

→ Ca + O₂ → 2 CaO

Now right: Ca = 2, O = 2
Left: Ca = 1, O = 2

Calcium now unbalanced. Put 2 in front of Ca:

→ 2 Ca + O₂ → 2 CaO

Check:

Left: Ca=2, O=2
Right: Ca=2, O=2

✔ Balanced!

Coefficients: 2, 1, 2

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Third equation: N₂ + H₂ → NH₃

Left:
N = 2
H = 2

Right:
N = 1
H = 3

Pick nitrogen first. To get 2 nitrogens on right, put 2 in front of NH₃:

→ N₂ + H₂ → 2 NH₃

Now right: N=2, H=6
Left: N=2, H=2

Hydrogen unbalanced. Need 6 hydrogens on left. Since H₂ has 2 per molecule, we need 3 molecules: 3 × H₂ = 6 H

→ N₂ + 3 H₂ → 2 NH₃

Check:

Left: N=2, H=6
Right: N=2, H=6

✔ Balanced!

Coefficients: 1, 3, 2

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Fourth equation: Cu₂O + C → Cu + CO₂

Left:
Cu = 2
O = 1
C = 1

Right:
Cu = 1
O = 2
C = 1

Start with copper. Right has 1, left has 2 → put 2 in front of Cu:

→ Cu₂O + C → 2 Cu + CO₂

Now Cu: left=2, right=2 ✔
O: left=1, right=2 ✘
C: left=1, right=1 ✔

Need more oxygen on left. But Cu₂O only has 1 oxygen. So try putting 2 in front of Cu₂O:

→ 2 Cu₂O + C → 2 Cu + CO₂

Now left: Cu=4, O=2, C=1
Right: Cu=2, O=2, C=1

Copper now wrong — left=4, right=2 → fix right: put 4 in front of Cu:

→ 2 Cu₂O + C → 4 Cu + CO₂

Now Cu: 4=4 ✔
O: left=2, right=2 ✔
C: left=1, right=1 ✔

Wait — carbon is okay? Yes. Oxygen is okay? Yes. Copper is okay? Yes.

But let’s double-check:

Left:
2 Cu₂O → 4 Cu, 2 O
1 C → 1 C
Total: Cu=4, O=2, C=1

Right:
4 Cu → 4 Cu
1 CO₂ → 1 C, 2 O
Total: Cu=4, C=1, O=2

✔ All match!

Coefficients: 2, 1, 4, 1

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Fifth equation: H₂O₂ → H₂O + O₂

Left:
H = 2
O = 2

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

Oxygen unbalanced.

Try putting 2 in front of H₂O₂:

→ 2 H₂O₂ → H₂O + O₂

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

Try putting 2 in front of H₂O:

→ 2 H₂O₂ → 2 H₂O + O₂

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

✔ Perfect!

Check:

Left: 2 H₂O₂ → 4 H, 4 O
Right: 2 H₂O → 4 H, 2 O; plus O₂ → 2 O → total O=4

Yes!

Coefficients: 2, 2, 1

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Now fill in all blanks from top to bottom.

Top paragraph:

Atoms are not created or destroyed during a chemical reaction.
Scientists know that there must be the same number of atoms on each side of the equation.
To balance the chemical equation, you must add coefficients in front of the chemical formulas in the equation. You cannot change or alter subscripts!

Then the example:

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

Then “Try these”:

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

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

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

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

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Final Answer:

Top blanks: created, destroyed, same, side, equation, coefficients, change, alter

Example: 2, 1, 2

Try these:
1. 2, 1, 2
2. 1, 3, 2
3. 2, 1, 4, 1
4. 2, 2, 1