Page 168 - text book form physics kssm 2020

Solving Problems Involving Pressure, Temperature and Volume of a Fixed Mass of
Gas Using Formulae from the Gas Laws
Example 1

Photograph 4.8 shows a syringe with its nozzle closed. Air in the
3
syringe has an initial volume of 7.5 cm and pressure of 105 kPa.
3
Th e air is compressed to a volume of 2.5 cm . What is the pressure
of the air?
Solution:
14243 P = compressed air pressure
1
Step P = 105 kPa Photograph 4.8
2
List the given information 3
in symbols. V = 7.5 cm 3
1
V = 2.5 cm
2
Step
Identify and write down the 123 P V = P V
1 1
2 2
formula used.
Step 105 × 7.5 = P × 2.5
2
Substitute numerical values into 14243 P = 105 × 7.5
the formula and perform the 2 2.5
calculations. = 315 kPa

Example 2

3
o
o
Air of volume 0.24 m in an expandable cylinder is heated from 27 C to 77 C at constant
o
pressure. What is the volume of the air at 77 C?
Solution:
V = 0.24 m 3 V 1 V 2
1
V = Final volume of air T 1 = T 2
2
T = (27 + 273)
1
= 300 K 0.24 = V 2

T = (77 + 273) 300 350
2
= 350 K V = 0.24 × 350
2
300
= 0.28 m 3

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