Aman Bansal
Last Activity: 12 Years ago
Dear Rahul,
The Individual Gas Laws
Historical laws were based on observations named for pioneers in gas experimentation.
The pressure/volume law is named after Robert Boyle, a British chemist, but the same law is called Mariotte’s Law in Europe after Edme Mariotte, a French chemist. Mariotte did similar experiments and reached the same conclusion as Boyle but slightly later. While most U.S. textbooks call the temperature/volume law Charles’ Law after Jacques Alexandre Charles, some give the credit to Joseph Gay-Lussac while others hedge and call it “Charles’ and Gay-Lussac’s Law.” Apparently, Charles did the research first (1787), but Gay-Lussac published first (1802). Credit could also be given to Guillaume Amontons, who, in 1702, invented a thermometer based on gas expansion. It wasn’t a very good thermometer, but his work was a hundred years earlier than Gay-Lussac’s.
The Law of Combining Volumes is sometimes referred to as Gay-Lussac’s Law. Gay-Lussac noted that when gases react to form a gaseous product, the ratio of the gas volumes form small whole numbers (this is similar to Dalton’s Law of Multiple Proportions for similar reasons). Avogadro used this data to support his hypothesis that, if two gases at the same pressure and temperature have the same volume, they must have the same number of particles. This idea lead to Avogadro’s Law, which everybody calls Avogadro’s Law; however, it could just as easily be named Gay-Lussac’s Law.
For most chemistry courses, your instructor will not require that you know which scientist formulated which law, how he did it, and when (especially since there isn’t uniform agreement on who gets credit for which law). All instructors will expect that you understand and remember the principles of all of the laws.
Boyle’s Law, Pressure and Volume
This gas law was the earliest, 1662, because air pumps and manometers were invented before a calibrated thermometer.
If temperature and amount of gas are kept constant, the pressure and volume are inversely proportional. This can be expressed mathematically as
where P and V are the pressure and volume of a gas and c is a proportionality constant. It is possible to calculate the resulting volume (or pressure) as pressure (or volume) changes if one knows the initial volume and pressure.
P1V1=P2V2
In observational terms, if the pressure increases, the volume of a gas must decrease, and vice versa. People who live in the mountains are familiar with this phenomenon. Bags of chips are packaged at close to sea level then shipped up to the mountains where the air pressure is much lower. The air in the sealed bags expands to make little chip filled balloons.
A typical freshman chemistry or physics experiment on Boyle’s Law will have a pressure gauge connected to a large syringe. Students change the volume of air trapped in the syringe by depressing or pulling out the plunger, which changes the pressure of the gas trapped inside. A graph of pressure and the reciprocal of the volume of the gas will be a straight line. In the middle of the seventeenth century, Robert Boyle wasn’t lucky enough to have digital pressure gauges and plastic tubing. He performed his gas experiments using air trapped in a u-shaped glass tube by a mercury plug. Pouring additional mercury into the tube increased the pressure and decreased the volume of the trapped gas.
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Thanks
Aman Bansal
Askiitian Expert
