Boyle’s Law in Simple Words

Learning Objective

• understanding Boyle’s Law concept
• Boyle’s law Formula and Derivation
• Boyle’s Law Graphical Representation
• Boyle’s Law Experiment
• Boyle’s law real life examples

Boyle’s Law Statement

According to Boyle’s Law, “at a constant temperature, the volume of a fixed mass of a gas is inversely proportional to its pressure.” This statement describes the relationship between volume and pressure.

Mathematically

     PV  = Constant    —–(A)

Equation (A) shows that at a constant temperature the product of pressure and volume (PV) of a gas remains constant.

Boyle’s Law Formula and Derivation

Any change in the volume occupied by a gas (at constant quantity and temperature) will result in a change in the pressure exerted by the gas, according to Boyle’s law. In other words, the product of a gas’s starting pressure and initial volume is the same as its final pressure and final volume (at constant temperature and number of moles). This law can be mathematically represented as follows:

For two states of a gas at a constant temperature, we can write

P1V1=constant —-(i) (For state 1)

P2V2=constant —-(ii) (For state 2)

Comparing equation (i) and(ii), we get

P1V1= P2V2 —–(B)  (T= constant)

Boyle’s Law Graphical Representation

Graphically, a plot of volume against the pressure of a gas at a constant temperature(isotherm) is a hyperbola while a plot of volume against 1/P is a straight line.

Boyle’s Law Experiment :

Consider a gas in a cylinder of the movable piston and provided with a manometer, at a constant temperature.

When the external pressure on the piston is doubled by placing more weight, the pressure of the gas is also doubled and volume is halved.

Similarly, by tripling the pressure, the volume of a gas is reduced to one-third and so on.

When the volume of a gas decreases, the number of collisions per second increases i.e. pressure of a gas increases and vice versa.

Boyle’s Law Real Life Examples

When you pump air into your bicycle tyres, you can notice an application of Boyle’s Law. When air is pumped into a tyre, the gas molecules within the tyre become compressed and more closely packed. This increases the gas pressure, which begins to push against the tire’s sidewalls. The tyre becomes increasingly pressured and tighter. A second illustration is a Coke bottle. Typically, the entire bottle is compressed with gas to inject carbon dioxide into the liquid. As long as the bottle is sealed, it is very difficult to squeeze because the gas is trapped in a tiny space and presses against the walls of the bottle. However, when the cap is removed, the accessible volume increases and some gas escapes. Simultaneously, its pressure falls.

Our breathing is an essential demonstration of Boyle’s law. Essentially, inhaling and exhaling involve expanding and contracting the chest cavity. This causes low pressure and high pressure in our lungs, causing air to be sucked into and expelled from our lungs, respectively. In this project, you will design your own Boyle’s law demonstration.

Materials

At least two little balloons, such as water balloons, are displayed.
Large plastic syringe (about 60 millilitres works nicely), such as an oral medication syringe for youngsters (available at most drug stores). Make certain it is airtight and lacks a needle.
Scissors
Scissors

Preparation

Use the syringe to inflate one balloon with a small amount of air so that it will still fit into the syringe. Finish the balloon by tying it off and trimming any excess material beyond the knot.
The syringe is filled with water.
Use the syringe to fill a second balloon with water to the same size as the first air-filled balloon. After tying the opening with a knot, cut away any excess cloth.
Remove the plunger from the syringe so the big end is exposed.

Procedure

Place the air-filled balloon just within the back of the syringe’s wide hole. Insert the plunger into the syringe and attempt to insert the balloon into the syringe’s tip. How difficult is it to insert the plunger? What occurs to the air contained within the syringe?
Pull the plunger back and position the balloon in the syringe’s centre. Then, using one finger, shut the front opening (the tip) of the syringe and reinsert the plunger. What do you notice? How does the balloon appear or change as the plunger is depressed?
Release your finger from the syringe’s tip. Insert the balloon into the syringe’s tip, and then push the plunger until it reaches the balloon. Then, close the syringe’s tip with your finger and fully retract the plunger. Does the shape of the balloon change? If yes, then how? Can you elaborate?
Replace the air-filled balloon with the water-filled balloon within the syringe. Then, the plunger is inserted into the syringe. Close the syringe’s tip with your finger and press the plunger as far as possible into the syringe. How does the balloon evolve this time around?
Release your finger from the tip of the syringe and push the plunger until it contacts the balloon at the tip. Then, close the syringe’s tip with your finger and attempt to pull the plunger as far back as possible. What happens to the balloon filled with water? Does it act differently than a balloon filled with air? If so, then how and why?
Extra: In addition to the air-filled and water-filled balloons, add water to your syringe. Then, close the syringe’s tip and attempt to press the plunger into the syringe and withdraw it again. What transpires now? What difference does the water within the syringe make?

Observations and Conclusions

Did you observe the air within the balloon grow and contract?
Without closing the syringe’s tip with your finger, the plunger can be readily depressed. The aperture at the tip of the needle allows air to escape. However, after you seal the syringe with your finger, air cannot escape. By depressing the plunger, you raise the air pressure, causing the air in the balloon to compress and reduce in volume. You should have observed the air-filled balloon shrinking and becoming smaller. When the syringe’s opening is sealed and the plunger is retracted, the opposite occurs. This time, you reduce the air pressure inside the syringe, causing its capacity to increase. The resulting expansion and growth of the air-filled balloon is a superb illustration of Boyle’s law!

The results alter when the balloon is filled with water. Although the air inside the syringe is compressed when the plunger is depressed, the water inside the balloon is not compressed. The balloon’s size remains unchanged. The water balloon also retains its shape when the plunger is withdrawn while the syringe tip is closed. Unlike gases, liquids cannot be compressed because their particles are already so close together. Boyle’s law applies exclusively to gases.

If you also filled the syringe with water, the air-filled balloon should have shrunk when you pushed the plunger into the syringe. The air-filled balloon should have expanded when the plunger was withdrawn from the syringe while the needle tip was closed. You may have observed, however, that you could not push and draw the plunger as far as you could with the air-filled syringe. This is due to the fact that, unlike gases, liquids cannot be compressed. You should have also witnessed this when attempting to insert or remove the plunger from the water-filled syringe with the water-filled balloon. Almost certainly, it was difficult to move the plunger in and out!

Frequently Asked Questions – FAQs

Can Boyle’s law be demonstrated experimentally?

Boyle’s law is a relationship between volume and pressure. It states that, under constant temperature, the pressure of a particular quantity of gas is inversely proportional to its volume. The law can be demonstrated empirically. The study discusses a syringe-based experimental method for establishing the validity of the legislation.

What is the law of Boyle?

Robert Boyle, an Anglo-Irish scientist, formulated Boyle’s law in 1662. At a constant mass and temperature, he asserted that the pressure exerted by a gas is inversely proportional to the volume it occupies.

What is the link between volume and pressure?

Boyle’s law states that the pressure and volume are inversely proportional to one another.
P ∝ (1/V)

Why does greater pressure cause a decrease in volume?

Due to the increased proximity of gas particles as pressure increases, volume decreases with rising pressure. Similarly, volume increases when pressure decreases because the gas particles get more distant from one another.

What is the effect of doubling the volume on the pressure?

For gas with a constant mass and temperature, the pressure is inversely proportional to its volume. If the volume is doubled, the pressure will decrease by one-half.
Why doesn’t Boyle’s law apply at high pressure?
Boyle’s law only applies at low pressure because at high pressure, gases behave like ideal gases.

How does Boyle’s law work?

Boyle’s law asserts that the pressure and volume of a gas are inversely related. When temperature remains constant, as volume increases, pressure decreases, and vice versa.

Why is Boyle law important?

Boyle’s law is significant because it describes the behaviour of gases. It demonstrates conclusively that gas pressure and volume are inversely proportional. When pressure is applied to a gas, the volume decreases and the pressure rises.

What is the formula for Boyle’s gas law?

As suggested by scientist Robert Boyle in 1662, the empirical relation says that the pressure (p) of a given quantity of gas varies inversely with its volume (v) under constant temperature; i.e., pv = k, a constant.

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