JSS 3: BOYLE'S LAW
BOYLE'S LAW states that the volume of a given mass of a gas is inversely proportional to the pressure provided the temperature remains constant.
Proportional Relationship:
V ∝ 1/P (V is inversely proportional to P)
V = k/P
P V = k
where: P = Pressure, V = Volume
k = a constant value for a given sample of gas at a constant temperature.
P₁V₁ = k and P₂V₂ = k, we can set them equal to each other. This gives us the most practical form of Boyle's Law:
P₁V₁ = P₂V₂
Where:
P₁ and V₁ are the initial pressure and volume.
P₂ and V₂ are the final pressure and volume.
Graphs of Boyle's law
1. When the pressure on a gas increases at constant temperature, the volume will (a) increase (b) decrease (c) remain constant (d) first increase then decrease
2. The volume of a given mass of a gas at 10oC and 600mmHg is 140cm3. What will be the volume of the gas at 10oC, if the pressure is 1200mmHg.
Solution:
P1V1 = P2V2
600 x 140 = 1200 x V2
84000 = 1200 x V2
V2 = 84000 / 1200
V2 = 70cm3
3. A sample of oxygen gas has a volume of 220 mL when its pressure is 2.2 atm. What will the volume of the gas be at a pressure of 1.2 atm if the temperature remains constant?
Solution:
Initial Volume (V1 ) = 220 mL
Initial Pressure (P1 ) = 2.2 atm
Final Pressure (P2 ) = 1.2 atm
To Find: Final Volume (V 2 ) = ?
We can calculate the final volume of the gas using Boyle’s law.
P1 V1 = P2 V2
2.2 X 220 = 1.2 X V 2
484 = 1.2 X V 2
484 / 1.2 = V 2
V 2 = 403.33 mL ≈ 403mL
Class activities
A certain volume of a gas at 20oC has a pressure of 400mmHg. If at the same temperature, this pressure is decreased to 200mmHg, the gas has now occupying a volume of 100cm3. Calculate the initial volume of the gas.
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