Boyle’s law states that at a constant temperature, the volume of a gas is inversely proportional to the pressure exerted by the gas. Boyle proved this by pumping oxygen into a sealed glass tube with varying amounts of mercury. Real-world examples include balloons and syringes. The law of Charles and Gay-Lussac shows that the volume of a gas changes with temperature.
Boyle’s law is a fundamental law of chemistry that describes the behavior of a gas held at a constant temperature. The law, discovered by Robert Boyle in 1662, states that at a fixed temperature, the volume of gas is inversely proportional to the pressure exerted by the gas. In other words, when a gas is pumped into an enclosed space, it will shrink to fit that space, but the pressure the gas exerts 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 experiment
To prove 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 then poured varying amounts of mercury into the tube, which varied the pressure on the oxygen. He found that the more pressure he applied, the smaller the volume of oxygen and this reduction occurred at a constant rate.
Boyle’s law specifically refers to an ideal gas, which is a theoretical gas composed of random particles that do not interact. While no real gas is an ideal gas, 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 that air – a gas – pushes on the rubber, causing the balloon to expand. If one end of the balloon is squeezed, reducing the volume, the pressure inside rises, causing the unsqueezed part of the balloon to expand. There is a limit to how much the gas can be compressed, however, because eventually the pressure becomes so great that it causes the balloon (or any container) to rupture.
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 inserted into anything, the volume of the tube will increase and the pressure will decrease, allowing more air into the tube to equalize the pressure. If the syringe is inserted into a vein and the plunger is pulled back, blood will flow into the tube because the pressure in the vein is higher than the pressure in the syringe.
Another way to describe Boyle’s law is that when pushed, a gas tends to repel. Without the massive amount of gravity holding them together, the solar system’s gaseous planets would spread rapidly in all directions, rapidly depressurizing themselves. In this case, the pressure of gravity regulates the volume of gases around these planets.
The law of Charles and Guy-Lussac
The inverse of Boyle’s law is the law of Charles and Gay-Lussac, 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 constant temperature and pressure change, Charles and Gay-Lussac’s law focuses on temperature change.
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