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Grades 9 and 10 Intermediate About 20 min Version 1 Awaiting review Premium

Balancing chemical equations

In a chemical reaction the atoms of the reactants are rearranged to make the products. No atoms are created or destroyed, so the total mass stays the same (the law of conservation of mass). A chemical equation must therefore be balanced: the same number of each kind of atom on both sides. You balance an equation by changing the big numbers (coefficients) in front of each formula. You must never change the small numbers inside a formula, because that would change the substance itself.

What you will learn

  • Count the atoms of each element on both sides of an equation.
  • Balance simple equations by changing coefficients.
  • Explain why equations must balance, using conservation of mass.

Before you start

  • Read chemical formulae such as H₂O and CO₂.

Materials

  • Molecular model kit or coloured beads (optional)

Equipment

  • None

Procedure

  1. Choose the hydrogen reaction. Change the coefficients until every atom tally shows a tick, and record it.
  2. Balance the methane and magnesium reactions.
  3. Balance the rusting of iron and the photosynthesis equation.

How this simulation is simplified

  • Only whole-number coefficients from 1 to 6 are offered; the fourth coefficient is ignored when there is no fourth substance.