Thermal decomposition gas volumes from stoichiometry

Steps:

• CaCO₃ → CaO + CO₂, so 0.005 mol produces 0.005 mol CO₂ gas = 100 cm³.
• Molar gas volume = 100 cm³ / 0.005 mol = 20,000 cm³/mol.
• Ca(NO₃)₂ → CaO + 2NO₂ + ½O₂, so 1 mol produces 2.5 mol gas.
• 0.005 mol Ca(NO₃)₂ produces 0.005 × 2.5 = 0.0125 mol gas.
• Volume = 0.0125 mol × 20,000 cm³/mol = 250 cm³.

Why D is correct:

• Nitrate decomposition produces 2.5 mol gas per mol compound (2 NO₂ + 0.5 O₂), 2.5 times the 1 mol from carbonate, yielding 250 cm³ by Avogadro's law.

Why the others are wrong:

• A: 50 cm³ assumes 0.5 mol gas, opposite of actual 2.5 mol.
• B: 100 cm³ assumes 1 mol gas like carbonate, ignores extra from nitrate.
• C: 200 cm³ assumes 2 mol gas (just NO₂), misses 0.5 mol O₂.

Final answer: D