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Boyle’s Law

How many of you fell in love with ‘chemistry’ at first sight? I am expecting a variety of answers. Well, I did for sure. How fascinating is the fact that there are hidden theories behind everything we see, touch, and feel? Yeah right, the matter is all around us and there is a plethora of research to study. Well not only around us but chemistry is within us as well. Heard about constant chemical reactions in your body? Yes, there is the combustion and different chemical reaction of substances. All this sums up to, Chemistry is essential to understand the tricky world around us.

Chemistry laws

I think I won’t be wrong if I said most of our first real and intricate memories of chemistry have been the LAWS! Right! Just like me, I am sure all of you have had a hard time learning the statements and memorizing the weird equations. On top of it, the various conditions accompanied by it were never fun. However, later when you get acquainted with the laws I think it becomes pretty simple and precise. Well if you still not understand the theories behind it, you have arrived at the right place.

Today we will discuss the Boyle’s law in detail. If you go through the explanation carefully, the law won’t trouble you. I promise.

Discovery of Boyle’s law

We all are well aware that gases have mass and occupy space or say have volume. As far as pressure is concerned, gases exert pressure as well. Robert Boyle, an Anglo-Irish chemist studied and put forth this nature in the form of Boyle’s law in 1662. He discovered the law whilst an experiment with a J-shaped tube. He trapped a small amount of air above the mercury column. The volume is then measured at a particular atmospheric pressure and a constant temperature. The air decreased proportionately to the pressure produced.

You may observe in certain textbooks or a case study, Boyle’s law is also referred to as Boyle-Mariotte law. This is about a French physicist Edme Mariotte who in 1679 discovered the same law independently. They both derived the law solely by experiment.

Explanation of Boyle’s law

The statement of Boyle’s law gives us an understanding of how the relationship exists between the pressure and volume of a gas.

Boyle’s law states that,
‘For a given or fixed amount of ideal gas, the pressure exerted by the gas is inversely proportional to the volume occupied by the gas within a closed system at a fixed temperature.’

In other words, there exists an inverse relationship between the pressure and volume of a gas i.e. if one doubles the other is reduced to half. The observation of this law happens strictly within a closed system under some conditions that one is allowed not to compromise with. The conditions are – the amount of gas or number of molecules should be constant along with the temperature. Even if one condition does not sustain, Boyle’s law can’t be deduced.

Boyle’s law beautifully put forwards the relationship where one can understand the expansion and compression of the gas.

Boyle’s law equation

Laws have always been converted into the equations which are a simplified version easy to understand.

A simple law for ideal gas states that a change in pressure (P) will result in a change in volume (V) at constant mass and temperature (T) and this change is inversely proportional.

We can understand this by the following mathematical relationship,
P = (1/V)
P =  k(1/V)
P = kV
where k = constant,
P = pressure exerted by the gas
V = Volume occupied by gas
When the above terms are plotted in a graph, a straight line is observed in pressure against volume gas. Remember to take pressure exerted by the gas on the y-axis and the inverse volume (1/V) on the x-axis.

Boyle’s Law Derivation and Calculations

There is a fixed formula derived for Boyle’s law to do the calculations efficiently. As per the statement, change in pressure will inversely change the volume of gas. The above lines mean if we multiply the initial pressure and initial volume of the gas the product should be similar to the multiplication of final pressure and final volume.

This gives rise to the following terms that we can be expressed as,
P1 = initial pressure of the gas
V1 = initial volume of gas
P2 = final pressure of the gas
V2 = final volume of gas

Therefore, we can derive a mathematical formula of Boyle’s law for constant volume and temperature as,
P1V1 = k,
P2V2 = k,
P1V1 = P2V2

Applications of Boyle’s Law in daily life

In a balloon

Have you ever tried to blow a balloon or burst it? If yes, you might appreciate how Boyle’s law is behind it. When you blow the balloon you are inserting air and the surface of the balloon expands. This blown balloon when subjected to pressure, say you try squeezing it will decrease the volume of air inside. In simple terms, increasing the pressure will result in decreasing the volume, and the balloon may burst. This is Boyle’s law, the inverse relationship between pressure and volume.

Human lungs

An essential part of the human body is the human lungs. They do the two primary processes – inhalation and exhalation. When the lungs expand, the momentary pressure decreases. This results in the change of pressure outside and inside the body. During this, the pressure inside the body is lower than outside. Therefore to balance out, we inhale the surrounding air. Similarly, when lungs are relaxed, the pressure inside is high than outside and hence we exhale the air.

Soda bottle

We all know this one as this is a basic task we all have done. There is a sudden mess if we open the soda bottle quickly. This happens because the air is passed over the CO2 in the soda bottle when the soda is filled in it. When you try to open it, the pressure on the gas reduces and the volume of gas expands eventually. Therefore, always open the cap slowly so that the gas comes out quietly. This is how Boyle’s law works in soda bottles unknowingly.