Amount Of Substance (gases)

• Molar gas volume = volume per mole of gas molecules at a stated temperature and pressure (usually RTP)
• Room temp is about 20°C and 101KPa
• Molar gas volume = volume(dm3) / moles
• Ideal gas Exchange = pV = nRT

  p - pressure, Pa

  V - volume, m3

  n - moles, mol

  R - ideal gas constant, 8.314

  T - temperature, K
• cm3 - m3 = x10 -6

  dm3 - m3 = x10 -3

  °C - K = +273

  KPa - Pa = x10 3
• Molar Gas Volume at RTP is 24 dm3
• Stoichiometric ratio Question:

  Nitrogen fertiliser A has the composition of mass Na: 27.1% ; N: 16.5% ; O: 56.4%

  On heating, 3.40g of A decomposes into Sodium Nitrite, NaNO2 and oxygen gas

  • calculate empirical formula of A

  n(Na) = 27.1 / 23.0 = 1.18

  n(N) = 16.5 / 14.0 = 1.18

  n(O) = 56.4 / 16.0 = 3.53

  1.18:1.18:3.53

  1:1:3 NaNO3

  • Write an equation

  2NaNO3 -> 2NaNO2 + O2

  • Calculate volume of oxygen gas at RTP

  n(NaNO3) = 3.40 / 85 = 0.04

  n(O2) = 2:1 ratio = 0.04 / 2 = 0.02

  0.48dm3= 24 x 0.02