State Avogadro's law - Leaving Cert Chemistry - Question e - 2004

An ideal gas is a theoretical gas that perfectly follows the gas laws, specifically Boyle's law and the kinetic theory of gases, represented by the equation PV = nRT. In an ideal gas, it is assumed that there are no intermolecular forces and that the volume of the gas molecules themselves is negligible.

Ammonia gas deviates from ideal gas behaviour due to the presence of polar intermolecular forces, which arise from the significant attraction between ammonia molecules. This results in a volume that is not negligible and collisions that are not perfectly elastic.

To calculate the volume of propanone vapour formed:

1. Find the number of moles (n):

   • The molar mass of propanone (C3H6O) = 58 g/mol.
   • Given mass = 0.29 g.
   • Number of moles:

   $n = \frac{0.29 \text{ g}}{58 \text{ g/mol}} = 0.005 \text{ mol}$

2. Use the ideal gas equation:

   • Applying the ideal gas equation:

   $PV = nRT$

   • Where:
   • P = 101 kPa = 101,000 Pa,
   • R = 8.31 J/(mol·K),
   • T = 20 °C = 293 K.

3. Calculate the volume (V):

   • Rearranging the equation, we have:

   $V = \frac{nRT}{P} = \frac{0.005 \text{ mol} \times 8.31 \text{ J/(mol·K)} \times 293 ext{ K}}{101,000 \text{ Pa}}$

   • Performing the calculation:

   $V = 0.00012 \text{ m}^3 = 0.12 \text{ litres}$

   Therefore, the volume of propanone vapour formed is 0.12 litres.