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 10°C and 600mmHg is 140cm³. What will be the volume of the gas at 10°C, 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 (V₂) = ?
We can calculate the final volume of the gas using Boyle’s law.
P₁V₁ = P₂V₂
2.2 × 220 = 1.2 × V₂
484 = 1.2 × V₂
484 / 1.2 = V₂
V₂ = 403.33 mL ≈ 403mL
Class activities
A certain volume of a gas at 20°C 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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