S4.7.2 For the adult
Balancing equations
A candle burns away and leaves almost nothing. Where did the wax go?
What this chapter teaches
In a reaction atoms are only rearranged, so an equation must have the same atoms on both sides. We balance it with numbers in front of formulae and never change a formula. Mass is conserved, and an apparent change in an open container is a gas leaving or joining from the air.
Three questions to ask
There is no one right wording. Listen for the idea.
- Why can we write 2 in front of H₂O to balance an equation, but not change H₂O to H₂O₂?
- How would you check that 2Mg + O₂ → 2MgO is balanced?
- Why does magnesium weigh more after burning in an open dish, but chalk weighs less after heating?
After the chapter, the learner can
- Balance symbol equations and add state symbols
- Explain why mass is conserved in a reaction
What they copy into their notebook
Atoms are not made or destroyed, so both sides of an equation have the same atoms. Balance with numbers in front. Never change a formula. Mass is conserved.