Everything Science Grade 11

CHAPTER 5. THERMAL PROPERTIES AND IDEAL GASES 5.6

Therefore,

m = 0. 86 × 44 = 37. 84 g

Example 10: Ideal gas equation 3

QUESTION

1 mole of nitrogen (N 2 ) reacts with hydrogen (H 2 ) according to the following equation:

N 2 + 3H 2 → 2 NH 3

The ammonia (NH 3 ) gas is collected in a separate gas cylinder whichhas a volume of 25 dm^3.

The temperature of thegas is 22◦C. Calculate the pressure of the gas inside the cylinder.

SOLUTION

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

V = 25 dm^3

n = 2 (Calculate this bylooking at the mole ratio of nitrogen to ammonia,

which is 1:2)

T = 22◦C

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

V =

25

1000

= 0. 025 m^3

T = 22 + 273 = 295 K

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

variable.

pV = nRT

Therefore,

p =

nRT

V

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

p =

2 mol× 8. 3 J· K−^1 mol−^1 × 295 K

0. 025 m^3

= 195 880 Pa = 195. 89 kPa