Everything Science Grade 11

5.6 CHAPTER 5. THERMAL PROPERTIES AND IDEAL GASES

Example 11: Ideal gas equation 4

QUESTION

Calculate the number of moles of air particles in a 10 m by 7 m by 2 mclassroom on a day

when the temperature is 23 ◦C and the air pressure is98 kPa.

SOLUTION

Step 1 : Write down all the information that you knowabout the gas.

V = 10 m× 7 m× 2 m = 140 m^3

p = 98 kPa

T = 23◦C

Step 2 : Convert the known values to SI units if necessary.

p = 98× 1000 = 98 000 Pa

T = 23 + 273 = 296 K

Step 3 : Choose a relevant gas law equation that will allow you to calculate theunknown

variable.

pV = nRT

Therefore,

n =

pV

RT

Step 4 : Substitute the known values into the equation.Calculate the unknownvariable.

n =

98 000 Pa× 140 m^3

8. 3 J· K−^1 mol−^1 × 296 K

= 5584. 5 mol

Example 12: Applying the gas laws

QUESTION

Most modern cars are equipped with airbags for both the driver and thepassenger. An airbag

will completely inflate in 0,05 s. This is important because a typical car collision lasts about

0,125 s. The followingreaction of sodium azide (a compound found inairbags) is activated

by an electrical signal: