Chemical equations and conservation of mass
Answers are for parents and teachers.
1
Write in words what this equation says: 2Na + Cl₂ → 2NaCl.
Two atoms of sodium react with one molecule of chlorine to give two units of sodium chloride.
2
Balance: Mg + N₂ → Mg₃N₂. Show the atom count on both sides.
3Mg + N₂ → Mg₃N₂: 3 Mg and 2 N on each side.
3
Balance: C₃H₈ + O₂ → CO₂ + H₂O.
C₃H₈ + 5O₂ → 3CO₂ + 4H₂O.
4
In a closed system, copper reacts with 8 g of oxygen and 40 g of copper oxide forms. What mass of copper reacted?
40 − 8 = 32 g.
5
Find the mistake: “2H₂ + O₂ → 2H₂O is not balanced, because the molecule counts differ (3 and 2).”
Balanced means each element has the same number of atoms on both sides (4 H and 2 O). Molecule counts may differ.