Balance chemical equations
🎯 Try it
Single choice
Which part may change when balancing?
📝 Start by counting atoms
Change coefficients in front of formulae, never subscripts inside them. A subscript change creates a different substance.
Worked example: H₂ + O₂ → H₂O. Put 2 before H₂O to balance oxygen, then 2 before H₂: 2H₂ + O₂ → 2H₂O. Count: four H and two O atoms on each side.
✏️ Practice ladder
Keep every formula unchanged and choose the smallest whole-number coefficients.
1.
N₂ + H₂ → NH₃. Balance N first, then H.2.
Mg + O₂ → MgO.3.
CH₄ + O₂ → CO₂ + H₂O. Balance C, then H, then O.4.
Al + O₂ → Al₂O₃. Try a common multiple for oxygen.5.
Explain why changing MgO to MgO₂ is not a valid balancing step.These are paper exercises, not instructions to perform reactions.
🔑 Worked corrections
1.
N₂ + 3H₂ → 2NH₃: N = 2 and H = 6 on each side.2.
2Mg + O₂ → 2MgO: Mg = 2 and O = 2 on each side.3.
CH₄ + 2O₂ → CO₂ + 2H₂O: C = 1, H = 4, O = 4 on each side.4.
4Al + 3O₂ → 2Al₂O₃: Al = 4 and O = 6 on each side.5.
Changing a subscript changes the substance. Coefficients change how much of each unchanged substance is present.✅ Check your understanding
Single choice
In 2H₂O, how many hydrogen atoms are represented?
Single choice
Coefficient of O₂ in balanced methane combustion above?