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Balancing Chemical Equations: Count Atoms and Explain

Balance equations by counting each element, changing coefficients and explaining conservation of atoms. Includes a printable pair task.

Suggested: lower secondary chemistry; English A2 support • 20 minutes

Balance equations Printable student activity ↓

Your learning goal

Balance a simple reaction with whole-number coefficients and justify it using atom counts.

Understand the idea

A balanced equation has the same number of atoms of each element on both sides. Change coefficients in front of formulae; do not change the small subscripts inside a formula. A subscript change would describe a different substance.

A coefficient multiplies every atom in that formula. For example, 2H₂O contains four H atoms and two O atoms. Count one element at a time, then check all elements again.

Use the smallest whole-number ratio. The equation models conservation of atoms; it does not by itself tell you how fast a reaction happens or whether a visible change proves a particular product.

Worked example

  1. Start: H₂ + O₂ → H₂O. Oxygen is 2 on the left and 1 on the right.
  2. Put 2 before H₂O. The right now has H = 4 and O = 2.
  3. Put 2 before H₂. Result: 2H₂ + O₂ → 2H₂O. Both sides have H = 4 and O = 2.

Try it step by step

  1. Open Balance equations in Chemistry Lab. Predict coefficients before using hints.
  2. Adjust coefficients and compare the atom counts for each element.
  3. Try N₂ + H₂ → NH₃ and explain why you changed coefficients rather than formulae.
Balance equations

Printable student activity

Print this page to use the English-first worksheet. Teacher notes and answers are excluded.

CATCHIE · STUDENT ACTIVITY

Balancing Chemical Equations: Count Atoms and Explain

Name: ____________________ Class: __________ Date: __________

Goal: Balance a simple reaction with whole-number coefficients and justify it using atom counts.

  1. Balance: __ H₂ + __ O₂ → __ H₂O. List H and O counts on both sides.

  2. Balance: __ N₂ + __ H₂ → __ NH₃. Show your atom-count evidence.

  3. Explain: “I changed the coefficient of ___ because ___. I did not change the subscript because ___.”

https://catchie.link/en/topics/balancing-chemical-equations/

Teacher notes and sample answers

Water: 2, 1, 2 (H = 4 and O = 2 on each side). Ammonia: 1, 3, 2 (N = 2 and H = 6). Changing a subscript changes the chemical identity. Do this as a virtual or paper task, not a practical gas reaction.