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Chemistry · Grades 9–12

Balancing chemical equations

Study guide for Grades 9 to 12: 2 worked examples and 2 practice questions. Atoms are rearranged, not created or destroyed, so each element must appear the same number of times on both sides.

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Rule and key idea

Atoms are rearranged, not created or destroyed, so each element must appear the same number of times on both sides. Change only coefficients, never subscripts, and use the smallest whole numbers.

atoms of each element: left side = right side

Worked examples

Balance this equation using the smallest whole-number coefficients: __ Fe₂O₃ + __ CO → __ Fe + __ CO₂. What is the sum of all the coefficients?

Fe₂O₃ + 3 CO → 2 Fe + 3 CO₂: 1 + 3 + 2 + 3 = 9

9

Balance this equation using the smallest whole-number coefficients: __ Na + __ Cl₂ → __ NaCl. What is the coefficient of Cl₂?

2 Na + Cl₂ → 2 NaCl

1

Try two questions

  1. Balance this equation using the smallest whole-number coefficients: __ Al + __ HCl → __ AlCl₃ + __ H₂. What is the coefficient of Al?

  2. Balance this equation using the smallest whole-number coefficients: __ Na + __ Cl₂ → __ NaCl. What is the coefficient of Na?

Answers and reasoning

Answers and marking notes
  1. 2

    2 Al + 6 HCl → 2 AlCl₃ + 3 H₂

  2. 2

    2 Na + Cl₂ → 2 NaCl

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