To demonstrate the Law of Conservation of Mass, the total mass of the reactants must equal the total mass of the products. Let's analyze each equation.

1. 4 g H₂ + 61 g Cl₂ → 75 g HCl

   • Total mass of reactants: $4 \, \text{g} + 61 \, \text{g} = 65 \, \text{g}$
   • Total mass of products: $75 \, \text{g}$
   • Not conserved, because $65 \, \text{g} \neq 75 \, \text{g}$.

2. 12 g C + 22 g O₂ → 44 g CO₂

   • Total mass of reactants: $12 \, \text{g} + 22 \, \text{g} = 34 \, \text{g}$
   • Total mass of products: $44 \, \text{g}$
   • Not conserved, because $34 \, \text{g} \neq 44 \, \text{g}$.

3. 23 g Na + 12 g H₂O → 40 g NaOH + 1 g H₂

   • Total mass of reactants: $23 \, \text{g} + 12 \, \text{g} = 35 \, \text{g}$
   • Total mass of products: $40 \, \text{g} + 1 \, \text{g} = 41 \, \text{g}$
   • Not conserved, because $35 \, \text{g} \neq 41 \, \text{g}$.

4. 10 g H₂ + 46 g N₂ → 56 g NH₃

   • Total mass of reactants: $10 \, \text{g} + 46 \, \text{g} = 56 \, \text{g}$
   • Total mass of products: $56 \, \text{g}$
   • Conserved, because $56 \, \text{g} = 56 \, \text{g}$.

Thus, the reaction 10 g H₂ + 46 g N₂ → 56 g NH₃ demonstrates the Law of Conservation of Mass.

Would you like more details or have any questions?

Here are some related questions:

1. How can the Law of Conservation of Mass be violated in a chemical reaction?
2. What are some common types of reactions where mass appears to change?
3. How does the Law of Conservation of Mass apply in open systems?
4. How do scientists measure mass changes in real-life chemical reactions?
5. How does the Law of Conservation of Mass relate to energy conservation in reactions?

Tip: When calculating mass, always ensure all reactants and products are accounted for, including gases.