Have you ever noticed how a balloon gets smaller when you squeeze it? That’s actually a real-life example of Boyle’s Law in action! Boyle’s Law explains the relationship between the pressure and volume of a gas. It’s one of the basic gas laws you’ll come across in chemistry, and it helps us understand how gases behave when we change their surroundings. In this article, we’ll break down what Boyle’s Law means, go over its formula, explore where it's used in everyday life, and solve a few easy examples to help you get the hang of it. Whether you’re preparing for exams or just curious, this guide will make learning Boyle’s Law simple and clear.

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What is Boyle’s Law?

Boyle’s Law tells us how the pressure and volume of a gas are connected. It says that if you keep the temperature the same and don’t add or remove gas, then when you increase the pressure on a gas, its volume goes down, and when you reduce the pressure, the volume goes up. In simple words, pressure and volume move in opposite directions. This relationship was discovered by Robert Boyle, a scientist in the 1600s, which is why the law is named after him. It’s an important concept in chemistry and helps explain how gases behave in different situations.

Boyle’s law can be stated as at constant temperature, the pressure of a fixed amount of gas (i.e the number of moles “n”) varies inversely with its volume. Its formula can be written as,

P∝1/V

Where P = pressure of the gas.

V = volume of gas.

Where temperature T and moles of gas “n” are constant.

Hence this equation can be written as

P=k⋅1/V

Where k is the proportionality constant. The value of k depends on the amount of gas used, temperature of the gas and the units in which pressure and volume are expressed.

On rearranging the same equation we get, PV = k

Which means at constant temperature, the product of the pressure and volume of a fixed amount of gas is always constant. Consider a fixed amount of gas, at a constant temperature (T) which has volume V1 at pressure P1. After expansion, the new volume would be V2 and P2

So according to Boyle’s law,

P1V1=P2V2

P1/P2=V2/V1

This is the quantitative statement at constant temperature (T) and obeys the ideal gas equation at low pressure.

Boyle’s Law Graph 

There are two conventional graphs to represent Boyle’s law

• Pressure v/s volume.
• Pressure v/s volume⁻¹

Graph 1 – Pressure v/s Volume: 

• Represents graph of question pV=K.
• The value of K is different for each mass of gas, it varies only with respect to temperature.
• Each curve represents a different value of temperature and it is known as isotherm.
• Higher the curves higher is the temperature.
• If the pressure on the gas is halved then the volume of the gas doubles.

Graph 2 – Pressure v/s Volume⁻¹

• P=k⋅1/V with straight lines almost emerging from the same origin.
• At higher pressure gases deviate from this law and under those conditions we don’t get a straight line.
• We also observe that these gases are highly compressible, the same number of molecules occupy a smaller space.

• We can obtain a relationship between the pressure and density of a gas by Boyle’s law : density “d” is the ratio of mass (m) to its volume (v) 

d=mV

Substituting the value for “V”

d=m/k1⋅p = k’p

This shows at a constant temperature, pressure is directly proportional to the density of a fixed mass of the gas.

Boyle’s Law Applications

Boyle’s Law has many practical uses in our daily lives and in various fields like medicine, engineering, and space science. Let’s look at some common situations where this gas law is applied.

• A medical syringe is a classic example of Boyle’s law, where the gas (or air) is compressed on application of external pressure under normal temperature conditions.
• Inflation of tyres.
• Spray paints and aerosol sprays.
• Suits of astronauts are designed on the same principle.
• Biological functions like breathing are also based on the same.

Boyle’s Law Limitations

While Boyle’s law is helpful, it doesn’t work in every situation. It only applies to ideal gases, which are a simplified version of how real gases behave. The law also assumes that the temperature stays constant if the temperature changes, the results won’t be accurate. Lastly, at very high pressures or very low temperatures, real gases don’t follow Boyle’s Law exactly and may behave differently.

Solved Examples on Boyle’s Law

Example 1. A gas occupies 200ml at pressure of 1 bar at 30℃. How much volume will it occupy at the same temperature if the pressure becomes 1.025 bar?

Solution 1. Given data ,

Pressure (P1) = 1 bar.

Pressure (P2) = 1.025 bar.

Volume (V1) = 200 ml.

To find – Volume (V2)

According to Boyle’s law, at constant temperature,

P1V1=P2V2

1 x 200 = 1.025 x V2

200/1.025

= 195.12 ml

The changed volume of gas at new pressure = 195.12 ml

Example 2. What will be the minimum pressure required to compress 500 dm3 of air at 1 bar to 200 dm3 at 30℃?

Solution 3. Given data,

Volume (V1) = 200L

Pressure (P1) = 800kPa

Volume (V2) = 900L

To find Pressure (P2) 

According to Boyle’s law, from the given data,

P1V1=P2V2

800 x 200 = 900 x P2

P2=800×200900

New pressure (P2) = 177.77 kPa.

The new pressure for volume 900L of gas is 177.77 kPa.

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