Why do we balance a chemical equation? Name and state the law that suggests the balancing of a chemical equation? Balance the following chemical equation :
Zn + H₃PO₄ → Zn₃(PO₄)₂ + H₂
Generated by claude-sonnet-4-6 · 2026-06-14 10:29 · grounding rag
Model Answer
Why we balance a chemical equation:
A chemical equation is balanced to satisfy the Law of Conservation of Mass.
Law: Mass can neither be created nor destroyed in a chemical reaction. Therefore, the number of atoms of each element must be the same on both sides (reactant and product side) of the equation.
Balancing the equation:
Unbalanced: $\text{Zn} + \text{H}_3\text{PO}_4 \rightarrow \text{Zn}_3(\text{PO}_4)_2 + \text{H}_2$
Count atoms:
- Zn: LHS = 1, RHS = 3 → put coefficient 3 before Zn
- PO₄: LHS = 1, RHS = 2 → put coefficient 2 before H₃PO₄
- H: LHS = 6 (2×3), RHS = 2 → put coefficient 3 before H₂
Balanced equation:
$$3\text{Zn} + 2\text{H}_3\text{PO}_4 \rightarrow \text{Zn}_3(\text{PO}_4)_2 + 3\text{H}_2$$
Verification: Zn=3, H=6, P=2, O=8 on both sides. ✓
Source: Chapter 1, Section 1.1.2
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Explanation
- 1 mark for stating the reason (Law of Conservation of Mass).
- 1 mark for naming and stating the law correctly.
- 1 mark for the correctly balanced equation.
- Always verify atom count on both sides — examiners check this. Use only coefficients, never change subscripts inside formulae.