Everything Science Grade 11

CHAPTER 5. THERMAL PROPERTIES AND IDEAL GASES 5.5

Example 5: General Gas Equation 1

QUESTION

At the beginning of a journey, a truck tyre has avolume of 30 dm^3 and an internal pressureof

170 kPa. The temperature of the tyre is 16◦C. By the end of the trip, the volume of the tyre

has increased to 32 dm^3 and the temperature ofthe air inside the tyre is 35 ◦C. What is the

tyre pressure at the endof the journey?

SOLUTION

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

p 1 = 170 kPa and p 2 =?

V 1 = 30 dm^3 and V 2 = 32 dm^3

T 1 = 16◦C and T 2 = 40◦C

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

Here, temperature mustbe converted into Kelvin, therefore:

T 1 = 16 + 273 = 289 K

T 2 = 40 + 273 = 313 K

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

variable.

Use the general gas equation to solve this problem:

p 1 × V 1

T 1

=

p 2 × V 2

T 2

Therefore,

p 2 =

p 1 × V 1 × T 2

T 1 × V 2

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

p 2 =

170 kPa× 30 dm^3 × 313 K

289 K× 32 dm^3

= 173 kPa

The pressure of the tyreat the end of the journeyis 173 kPa.