Gas Volume Calculation - 1

Question: Calcium carbonate decomposes on heating. What volume of carbon dioxide, measured at room temperature and pressure (rtp), is produced when 5.00 g of calcium carbonate is completely decomposed? (A_r: Ca = 40, C = 12, O = 16; molar volume at rtp = 24 dm³ mol^-1)CaCO₃(s) → CaO(s) + CO₂(g)At rtp, one mole of any gas occupies 24 dm³, so:volume of gas (dm³) = moles × 24Step 1: moles of the substance you know.M_r(CaCO₃) = 40 + 12 + (3 × 16) = 100
n(CaCO₃) = 5.00 ÷ 100 = 0.0500 molStep 2: use the equation to find moles of gas. The ratio CaCO₃ : CO₂ is 1 : 1.n(CO₂) = 0.0500 molStep 3: convert moles to volume.V = 0.0500 × 24 = 1.20 dm³Since 1 dm³ = 1000 cm³, this is 1200 cm³.Going the other way: to find moles from a gas volume at rtp, divide by the molar volume: n = V (dm³) ÷ 24, or n = V (cm³) ÷ 24 000.Always check the units in the question. A common mistake is to divide a volume in cm³ by 24, which gives an answer 1000 times too large.