Robert Boyle’s Law

Boyle’s Law

(Relationship Between Volume and Pressure)

Robert Boyle was a famous chemist born in 1627 at Lismore Castle, Ireland. In his early years, he was tutored at home, and later went into the renowned Oxford University. His famous scientific paper that was published include New Experiments Physico-Mechanicall, Touching the Spring of the Air and Its Effects (1660), Sceptical Chymist (1661), and etc. He is especially famous for developing the Boyle’s Law.

Boyle’s Law: In 1662, Robert Boyle stated that the volume of a given amount of gas, at a constant temperature, varies inversely with the applied pressure. This means, as external pressure on a gas increases, the volume of the gas decreases by the same factor. Therefore, it is correct to say the volume and pressure of a certain quantity of a gas are inversely proportional.

Pressure: P Volume: V Constant: K

Pressure = Constant/Volume
or
Volume = Constant/Pressure
or
Pressure x Volume = Constant àPV=K

Equation : P₁ x V_{1 =} P₂ x V₂

Sample Questions

#1 A sample of nitrogen gas at 25°C is compressed from 250 cm³ to 0.180 cm³. Its pressure is now 2.50kPa. What was the original pressure of the nitrogen?

Given:
Initial volume V₁ = 250 cm³
Final volume V₂ = 0.180 cm³
Initial pressure P₂ = 2.50 kPa

Required:
the original pressure
P₁ = ?

Solution:
P₁V₁ = P₂V₂
P₁ = P₂V₂ / V₁
P₁ = 2.50kPa x 0.180 cm³/250 cm³
P₁ = 0.0018 kPa
P₁ = 1.8 x 10^-3 kPa
Statement:
Therefore, the original pressure of nitrogen gas is 1.8 x 10^-3 kPa

#2 The air in the bike has a pressure of 100kPa and 20L of air, after 2 pumps, the air in the tire went form 20L to 40L, what is the pressure now?

Given:Unknown:Equation: Solutions:

Pi=100kPa Pf=? PiVi=PfVf Let Pf be X.

Vi=20L 100×20=4xXFi=40L 100kPa20L=?4L 2000=4X

2000/4=4X/4

500=X

X=500 kPa

Statement:

Therefore, the air pressure in the tire now after the pump is 500 kPa.