The law of mass conservation states that mass is neither created nor destroyed in a chemical reaction. This means that the number of atoms of each element must be the same on both sides of the equation.
Let's analyze each equation:
A. H₂ + Cl₂ → HCl
- Reactants: 2 H, 2 Cl
- Products: 1 H, 1 Cl
- Not balanced.
B. H₂ + O₂ → H₂O
- Reactants: 2 H, 2 O
- Products: 2 H, 1 O
- Not balanced.
C. H₂ + O₂ → 2H₂O
- Reactants: 2 H, 2 O
- Products: 4 H, 2 O
- Not balanced.
D. H₂ + Cl₂ → 2HCl
- Reactants: 2 H, 2 Cl
- Products: 2 H, 2 Cl
- Balanced.
The equation that demonstrates the law of mass conservation is D. H₂ + Cl₂ → 2HCl, as both sides of the equation have the same number of atoms for each element.