8 gas calculations

• In order to perform calculations with gases we assume that they behave an ideal gas (I.e there are no forces between particles, the size of their particles is negligible etc)
• While real gases are not ideal gases (e.g there are weak forces forces between particels), treating them like an ideal gas is a very good approximation in calculations and so we use the ideal gas law for all gases
• Gas calculation equation =

  PV=nRT

  P= Pressure (Pa)

  V= volume (m³)

  n = number of moles

  R = gas constant = 8.31 Jmol-¹K-¹ (given in the exam)

  T = temperature (K)
• They could give volume in dm³ if so you need to do this

  dm³×10-³ = m³

  It could also give it in cm³ if so do this

  cm³×10-⁶ = m³
• They could give pressure in KPa if so do thus

  KPa × 10³ = Pa

  They could also give it to you in MPa if so do this

  MPa × 10⁶ = Pa
• They could give temperature in ºC if so do this

  ºC + 273 = K
• Example of a gas calculation

  Calculate the pressure exerted by 0.100 moles of an ideal gas at 50.0ºC with a volume of 1500cm³

  P = nRT ÷ V = (0.100 × 8.31 × 323) ÷ (1500 × 10-⁶) = 179000Pa (3sf)
• The volume of a gas depends on the temperature, pressure and number of moles. What the gas is does not affect its volume. This means that under the same conditions of temperature and pressure, 100cm³ (as an example) of one gas contains the same number of moles as 100cm³ of any other gas
• Examples of reacting gas volumes 1.What volume of oxygen reacts with 100cm³ of but-1-ene

  C4H8(g) + 6O2(g) -> 4CO2(g) + 4H20(l)

  answer = 600cm³

  2. 1dm³ of but-1-ene us reacted with 10dm³ of oxygen. What volume of volume of oxygen remins at the end

  C4H8(g) + 6O2(g) -> 4CO2(g) + 4H2O(l)

  6dm³ of O2 reacts with 1dm³ of but-1-ene therefore 4dm³ of oxygen is left over