# Boyle's law explained

### Boyle's Law:

Robert Boyle (1627-1691) is an English scientist who worked on confined gases in an attempt to discover the relationship between their pressure and volume at a constant temperature. During his work, he discovered that whenever he doubled the pressure of the gas, its volume decreases by the same amount.

According to Boyle's experiment, there is always an inverse relationship between the pressure and volume of a confined gas at a constant temperature. With regards to this inverse relationship, whenever the pressure increases, the volume decreases proportionately, and when volume increases, the pressure decreases by a similar amount.

Please the introduction to gas laws in chemistry here.

A graphical representation of Boyle's law is typically seen as a curve. This curve is called the PV (Pressure-Volume) curve, and it is hyperbolic in nature. It shows the relationship between the pressure of a gas and its volume at a constant temperature.

Below is a pressure-volume curve:

You can read on Le Chatelier's principle and dynamic equilibrium here.

From the above curve, notice that as the pressure decreases, the volume increases proportionately. This also implies that an increase in volume will result into a decrease in pressure. In this regard, the pressure and volume of a gas are always inversely proportional. Therefore, when one increases, the other must decrease according to Boyle's law.

Please on gaseous state of matter and their characteristics here.

The above image shows the volume of equal amount of a gas in different containers. You will observe that the gas within the first container has a lower pressure due to the container's large volume. For this reason, collision of gas molecules with the walls of the container and with the one another will be slower.

In this second container, the volume of gas was reduced by lowering the cork. This resulted into an increased pressure of gas within that container. Therefore, the gas molecules will collide more rapidly with themselves and the walls of the container.

Please read more on the kinetic theory of gases here.

Boyle's law states that the volume of a given mass of gas is inversely proportional to its pressure provided the temperature is remains constant. This law was formulated in 1662.

PV = K

You can read on Charles's law here.

Boyle's law is often referred to as Boyle–Mariotte law. In France, it is popularly referred to as Mariotte's law. The French physicist, Edme Mariotte (1620–1684) discovered the pressure-volume relationship in 1679.

Although, Boyle published his work in 1662, Mariotte made her discovery independently of Boyle. However, Mariotte further found out that the volume of air also changes with temperature.

The formula of importance for Boyle's law is:

• PV = k

• Where P = Pressure and V = Volume

• The k is a constant for a given sample of gas. It is dependent on the mass of the gas and its temperature.

You can read on Avogadro's number explained with worked examples here.

The formula for Boyle's law is often applied in solving questions involving the pressure or volume of a system at constant temperature. The formula is expanded below:

• PV = k

• P1V1 = P2V2

• P1 = Initial Pressure

• V1 = Initial Volume

• P= Final Pressure

• V2 = Final Volume

Please see worked calculations on Boyle's law here.

To further explain Boyle's law, recall that gas molecules exhibit random motion in a straight line since their particles are widely separated as a result of neglible cohesive forces between them. Therefore, increasing the pressure within the gas molecules pushes the molecules closer together, thus increasing their cohesive forces, and decreasing their occupied volume. If the pressure within the gas molecules are reduced, their occupied volume increases, and the gas will escape if an external outlet is present on the container. This instance is seen in aerosols and fire extinguishers.

Please read a detailed explanation on various examples of Boyle's law here.

Other instances of Boyle's law in real life include the following:

• Breathing in humans

• Inflating and deflating car tyres

• Skuba diving

• Opening a bottle of soda

• Use of a syringe

• Filling of balloons

• Deep-sea fishes

• Storage of gas

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