Volume of gas from a reacting mass

A-Level (AQA) · unreviewed

Mass of a carbonate decomposed; find the volume of gas at a stated temperature and pressure.

Worked example

Calcium carbonate decomposes on heating: CaCO₃ → CaO + CO₂. Calculate the volume, in cm³, of carbon dioxide formed from 3.61 g of CaCO₃ (M = 100.1 g mol⁻¹), measured at 296 K and 1.02 × 10⁵ Pa.

1. Moles from mass: solve for n(CaCO₃) = n(CO₂)
$n = \dfrac{m}{M}$
= 0.03606 mol
2. Ideal gas equation: solve for V(CO₂)
$V = \dfrac{nRT}{p}$
= 0.8702 dm³

Answer: V(CO₂) = 0.870 dm³

Method

n(CO₂) = n(CaCO₃) = m/M (1 : 1). Then V = nRT/p. In SI units p is in Pa and V comes out in m³; multiply by 10⁶ for cm³.

Formulas used

Moles from mass
$n = \dfrac{m}{M}$
Ideal gas equation
$pV = nRT$

Practise this with fresh numbers

Volume of gas from a reacting mass

Worked example

Method

Formulas used

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