Balancing Equations Worksheet - Free Printable

Let's solve this step by step.

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I. Fill in the blanks with the most appropriate term:

> A chemical equation tells the story of a chemical reaction. Reactants are the starting substances in the reaction while products are the new substances that are formed. The large numbers in front of some of the formulas are called coefficients. These numbers are used to balance the equation because chemical reactions must obey the Law of Conservation of Matter. The number of atoms of each element on both sides of the equation must be equal because matter cannot be created or destroyed. When balancing equations, the only numbers that can be changed are coefficients, remember that subscripts must never be changed in order to balance an equation.

✔ Explanation:
- A chemical equation represents a chemical reaction.
- Reactants go into the reaction; products come out.
- Coefficients are the numbers placed before formulas to balance atoms.
- The Law of Conservation of Matter states that matter is neither created nor destroyed in a chemical reaction.
- Therefore, atoms must be equal on both sides → we balance using coefficients.
- We never change subscripts (e.g., changing H₂O to H₃O would make a different compound), only coefficients.

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II. Balance the following equations:

#### 1. Al + O₂ → Al₂O₃

Step-by-step:

- Left side: Al = 1, O = 2
- Right side: Al = 2, O = 3

We need to balance Al and O.

- To get 2 Al on the left, use 2Al.
- To get 3 O on the right, but O₂ gives 2 O per molecule, find LCM of 2 and 3 → 6.

So:
- 3 O₂ → 6 O atoms
- 2 Al₂O₃ → 4 Al and 6 O

Now:
- Right: 4 Al, 6 O
- So left: 4 Al, 3 O₂

So:
→ 4Al + 3O₂ → 2Al₂O₃

✔ Balanced!

Check:
- Al: 4 = 4 ✔️
- O: 6 = 6 ✔️

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#### 2. C₄H₈ + O₂ → CO₂ + H₂O

This is a combustion reaction.

Unbalanced:
- C₄H₈ + O₂ → CO₂ + H₂O

Balance:
1. Carbon: 4 on left → 4 CO₂ on right
2. Hydrogen: 8 on left → 4 H₂O (since each has 2 H)
3. Now count O on right:
- 4 CO₂ → 8 O
- 4 H₂O → 4 O
- Total O = 12 → so need 6 O₂ (since each O₂ has 2 O)

So:
→ C₄H₈ + 6O₂ → 4CO₂ + 4H₂O

✔ Check:
- C: 4 = 4 ✔️
- H: 8 = 8 ✔️
- O: 12 = (4×2) + (4×1) = 8+4 = 12 ✔️

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#### 3. Al(NO₃)₃ + NaOH → Al(OH)₃ + NaNO₃

This is a double displacement reaction.

Unbalanced:
- Al(NO₃)₃ + NaOH → Al(OH)₃ + NaNO₃

Look at ions:
- Al³⁺ and NO₃⁻ from Al(NO₃)₃
- Na⁺ and OH⁻ from NaOH

Products: Al(OH)₃ and NaNO₃

Balance:
1. Al: 1 on both sides → OK
2. NO₃⁻: 3 on left → need 3 NaNO₃ on right
3. So: 3 NaNO₃ → need 3 Na⁺ → so 3 NaOH on left
4. Now OH: 3 NaOH → 3 OH⁻ → Al(OH)₃ needs 3 OH → OK

So:
→ Al(NO₃)₃ + 3NaOH → Al(OH)₃ + 3NaNO₃

✔ Check:
- Al: 1 = 1 ✔️
- N: 3 = 3 ✔️
- O: from NO₃ and OH — not needed if all others match
- Na: 3 = 3 ✔️
- H: 3 = 3 ✔️

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✔ Final Answers:

#### I. Fill in the blanks:
A chemical equation tells the story of a chemical reaction. Reactants are the starting substances in the reaction while products are the new substances that are formed. The large numbers in front of some of the formulas are called coefficients. These numbers are used to balance the equation because chemical reactions must obey the Law of Conservation of Matter. The number of atoms of each element on both sides of the equation must be equal because matter cannot be created or destroyed. When balancing equations, the only numbers that can be changed are coefficients, remember that subscripts must never be changed in order to balance an equation.

#### II. Balanced Equations:

1. 4Al + 3O₂ → 2Al₂O₃
2. C₄H₈ + 6O₂ → 4CO₂ + 4H₂O
3. Al(NO₃)₃ + 3NaOH → Al(OH)₃ + 3NaNO₃

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