#### 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

**Example**:

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

The pressure is measured as 145.60 kPa at a temperature of 25

^{o}C. What is the molar mass of the compound?

__Solution:__*Convert 225 mL to L; 225 mL = 0.225 L*

*Convert 25*

^{o}C to Kelvin; 25^{o}C = 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*

^{–2}mol*1.32*x

*10*

^{–2}mol = 0.580 g*! mol = x g*

*x g =*

__0.580 g____x__

*1 mol**= 44.0 g/mol*

*1.32*x

*10*

^{–2}mol**Activity - Solve the following problems:**

1. Calculate the volume of 36.0 g of steam at 115

^{o}C and 110.0 kPa of pressure.
2. If 28 g of N

_{2}, nitrogen gas, occupy 22.4 L at STP calculate the volume of 7 g of N_{2}at 0^{o}C and 202.6 kPa of pressure.
3. If 6 g of a gas occupy 20 L at 40

^{o}C 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

^{o}C, of the air in the tire.