Everything Science Grade 11

5.6 CHAPTER 5. THERMAL PROPERTIES AND IDEAL GASES

Example 9: Ideal gas equation 2

QUESTION

Carbon dioxide (CO 2 ) gas is produced as a result of the reaction between calcium carbonate

and hydrochloric acid. The gas that is produced is collected in a 20 dm^3 container. The

pressure of the gas is 105 kPa at a temperatureof 20^0 C. What mass of carbon dioxide was

produced?

SOLUTION

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

p = 105 kPa

V = 20 dm^3

T = 20◦C

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

p = 105× 1 000 = 105 000 Pa

T = 20 + 273 = 293 K

V =

20

1000

= 0. 02 m^3

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 =

105 000 Pa× 0. 02 m^3

8. 3 J· K−^1 · mol−^1 × 293 K

= 0. 86 mol

Step 5 : Calculate mass from moles

n =

m

M

Therefore,

m = n× M

The molar mass of CO 2 is calculated as follows:

M = 12 + (2× 16) = 44 g· mol−^1