An oil painting by Robert Boyle, after which Boyle’s Law is named.
Boyle’s Law is a basic law of chemistry that describes the behavior of a gas maintained at a constant temperature. The law, discovered by Robert Boyle in 1662, states that at a fixed temperature, the volume of the gas is inversely proportional to the pressure exerted by the gas. In other words, when a gas is pumped into a closed space, it will shrink to fit that space, but the pressure exerted by the gas on the container will increase. Boyle’s Law can be written mathematically:
P x V = constant
In this equation, P = pressure and V = volume.
Boyle’s experience
To test the law, Boyle pumped oxygen (a gas) into a J-shaped glass tube that was sealed at one end. Using a burner to keep the oxygen at a constant temperature, he poured different amounts of mercury into the tube, which varied the pressure of the oxygen. He discovered that the more pressure he applied, the lower the volume of oxygen, and this reduction occurred at a constant rate.
Boyle’s Law relates specifically to an ideal gas, that is, a theoretical gas that is made up of random, non-interacting particles. Although no real gas is ideal, most exhibit these ideal characteristics under normal conditions.
real world examples
An example of Boyle’s Law in action can be seen in a balloon. Air is blown into the balloon; the pressure of this air, a gas, pushes on the rubber and causes the balloon to expand. If one end of the balloon is compressed, making the volume smaller, the internal pressure increases, causing the uncompressed part of the balloon to expand. However, there is a limit to the amount of gas that can be compressed, because eventually the pressure becomes so great that it causes the balloon (or any container) to burst.
A different example is a syringe for drawing blood. An empty syringe contains a fixed amount of gas (air); if the plunger is pulled back without the end of the needle inserting into anything, the volume of the tube will increase and the pressure will decrease, causing more air to enter the tube to equalize the pressure. If the syringe is inserted into a vein and the plunger is withdrawn, blood will flow into the tube as the pressure in the vein is greater than the pressure in the syringe.
Another way to describe Boyle’s law is that when pushed, the gas tends to push back. Without the enormous amount of gravity holding them together, the solar system’s gaseous planets would spread rapidly in all directions, rapidly depressurizing. In this case, the pressure of gravity regulates the volume of gases around these planets.
Charles and Guy-Lussac Law
The inverse of Boyle’s Law is Charles and Gay-Lussac’s Law, named after the two French scientists who discovered it. Charles and Gay-Lussac’s Law shows that the volume of a gas increases or decreases with temperature. Written mathematically, the law looks like this:
V = constant x T
In this equation, V = volume and T = temperature. While Boyle’s Law focuses on the constant change in temperature and pressure, Charles and Gay-Lussac’s Law focuses on the change in temperature.