Question

1. choose the best answer.

which chemical equation demonstrates the law of conservation of mass?
4h₃po₄ → 3h₂o + p₄h₁₀
2no + o₂ → 2no
nai + cl₂ → i₂+nacl
4nh₃ + 5o₂ → 4no + 6h₂o

1. choose the best answer.

a reaction in which an electrical current is required is called ______.

electrolysis
catalytic reaction
dissociation
thermal decomposition

Explanation:

Question 16

Step1: Recall the law of conservation of mass (mass is conserved in a chemical reaction, so the number of each type of atom on the reactant side must equal the number on the product side).

Step2: Analyze each option:

• Option 1: \(4\ce{H3PO4} \to 3\ce{H2O} + \ce{P4H10}\)

Reactants: H: \(4\times3 = 12\), P: 4, O: \(4\times4 = 16\)
Products: H: \(3\times2 + 10 = 16\) (not equal to 12), so invalid.

• Option 2: \(2\ce{NO} + \ce{O2} \to 2\ce{NO}\) (product has same formula as one reactant, O atoms not conserved: reactants O: \(2 + 2 = 4\), products O: 2, invalid).
• Option 3: \(\ce{NaI} + \ce{Cl2} \to \ce{I2} + \ce{NaCl}\)

Reactants: Na: 1, I: 1, Cl: 2
Products: I: 2, Na: 1, Cl: 1 (Cl not conserved), invalid.

• Option 4: \(4\ce{NH3} + 5\ce{O2} \to 4\ce{NO} + 6\ce{H2O}\)

Reactants: N: 4, H: \(4\times3 = 12\), O: \(5\times2 = 10\)
Products: N: 4, H: \(6\times2 = 12\), O: \(4\times1 + 6\times1 = 10\) (all atoms conserved).

• Electrolysis is a reaction where an electric current is used to drive a non - spontaneous chemical reaction.
• Catalytic reaction: involves a catalyst (not electricity).
• Dissociation: separation of ions in solution (no electricity required).
• Thermal decomposition: decomposition due to heat (no electricity).

Answer:

\(4\ce{NH3} + 5\ce{O2} \to 4\ce{NO} + 6\ce{H2O}\) (the fourth option)

Question 17