Ideal Gas Law

Chemical reactions also involve substances in the gas phase, therefore to determine the number of moles of a gaseous compound the ideal gas equation is used
                        PV = nRT                    where P → pressure in kPa
                                                                      V → volume in litres (L)
                                                                      n → number of moles
                                                                      T → temperature in Kelvin (K)
                                                                      R → universal gas constant; 8.314 kPa • L• mol–1• K–1
-the ideal gas law can be used to determine any one of the variables from the knowledge of the other three
A glass bulb with a volume of 225 mL contains 0.580 g of an unknown gaseous compound.
The pressure is measured as 145.60 kPa at a temperature of 25 oC. What is the molar mass of the compound?
Convert 225 mL to L;  225 mL = 0.225 L
Convert 25 oC to Kelvin; 25 oC = 273 + 25= 298 K
Determine the number of moles of gas under the above conditions
n =PV = 145.0 kPa x 0.225 L
     RT     298 K x 8.314 kPa•L•mol–1•K–1
           = 1.32 x 10–2mol
1.32 x 10–2mol = 0.580 g
              ! mol  = x g
x g = 0.580 g x 1 mol  =  44.0 g/mol
        1.32 x10–2mol
Activity - Solve the following problems:
1.      Calculate the volume of 36.0 g of steam at 115 oC and 110.0 kPa of pressure.
2.      If 28 g of N2, nitrogen gas, occupy 22.4 L at STP calculate the volume of 7 g of N2 at 0 oC and 202.6 kPa of pressure.
3.      If 6 g of a gas occupy 20 L at 40 oC and 303.9 kPa of pressure, find its molar mass.
4.      A tire with a volume of 3.60 L contains 0.367 moles of air at a pressure of 252 kPa. What is the temperature, in oC, of the air in the tire.