What is Gas?
Gas is one of the three basic states of matter. The other two states are solid and liquid. These states differ from each other in the way they fill space and change shape. A solid, such as rock, always occupies a fixed volume (amount of space) and has a fixed shape. A liquid, such as water, always occupies a fixed volume. But it has no shape of its own, so it takes on the shape of its container. A gas, such as air, has neither a fixed shape nor a fixed volume. It fills any container that holds it and takes on the container's shape. Like solids and liquids, gases have weight. But gases are thinner and lighter than solids and liquids.
The Three Gas Laws
Three laws explain approximately how the pressure, temperature, volume, and the number of particles in a container of gas are related. These laws are Boyle's law, Charles's law, and Avogadro's law.
Robert Boyle
His Life
Boyle, Robert (1627-1691), an Irish scientist, is considered the founder of modern chemistry. He helped establish the experimental method in chemistry and physics.
Boyle is best known for his experiments on gases that led to the formulation of Boyle's law. This law says the volume of a gas at constant temperature varies inversely to the pressure applied to the gas. Boyle also helped improve the air pump, and with it he investigated the nature of vacuums.
Boyle introduced many new methods for determining the identity and chemical composition of substances. He disproved the theory that air, earth, fire, and water were the basic elements of all matter. Boyle argued that all basic physical properties were due to the motion of atoms, which he called "corpuscles."
Boyle lived in England for most of his life. He was a founding member of the Royal Society of London, one of the world's foremost scientific organizations. Boyle described his experiments in many books. He was born at Lismore Castle, Ireland.
Boyle's Law
The volume of a mass of gas at a fixed temperature will change in relation to the pressure. If the pressure on a gas increases, its volume will decrease. Volume is proportional to one divided by pressure.
Boyle's law was first published by the Irish chemist Robert Boyle in 1662. But other chemists had discovered the law earlier. In 1660 and 1661, Richard Towneley and Henry Power of England experimented with air below atmospheric pressure. They found that the product of the air's pressure and volume remained constant. At about the same time, Robert Hooke of England experimented with air above atmospheric pressure. Hooke's findings agreed with those of Towneley and Power. Additional experiments by Boyle confirmed all these findings. In 1679, Edme Mariotte of France published the results of his own experiments with gases. Mariotte's writings became well known in Europe. Thus, the law known today as Boyle's law in North America and Great Britain is called Mariotte's law in continental Europe.
Jacques Alexandres Charles
His Life
Jacques Alexandre Charles was a French chemist who worked on hydrogen balloons. Charles was assisted by two craftsmen, the brothers Anne-Jean and Marie-Noel Robert. Charles and the Robert brothers launched the first hydrogen balloon in Paris on Aug. 27, 1783. The balloon, which carried no passengers, was made of rubberized silk. It rose about 3,000 feet (900 meters) and landed in a field about 15 miles (25 kilometers) from the city.
Charle's Law
The volume of a mass of gas at a fixed pressure dpends on its temperature. The higher the temperature, the greater the volume. Volume is proportional to temperature.
Charles's law was discovered in 1787 by the French chemist Jacques Alexandre Cesar Charles. He found that carbon dioxide, hydrogen, oxygen, and nitrogen all expand at constant rates as their temperatures rise. Charles did not publish his findings, but explained his experiments to the French chemist Joseph Gay-Lussac. Gay-Lussac performed similar experiments and published his results in 1802. As a result, Charles's law is sometimes called Gay-Lussac's law.
Amedeo Avogadro
His Life
Amedeo Avogadro(1776-1856), was an Italian physicist born in Turin. He proposed in 1811 his famous hypothesis, now known as Avogadro's law. The law stated that equal volumes of all gases at the same temperature and pressure contain the same number of chemical units. Avogadro distinguished between gases composed of complex units (molecules) and gases made up of simple units (atoms). He was able to calculate atomic and molecular weights from gas densities. Avogadro's hypothesis was not accepted by the leading scientists of his time. His hypothesis was discounted until 1858, when Italian chemist Stanislao Cannizzaro reintroduced it and developed it further.
Avogadro's Law
The pressure exerted by a gas at constant volume increases as the temperature of the gas rises. Pressure is proportional to temperature.
The Universal Gas Law
The universal gas law combines Boyle's law, Charles's law, and Avogadro's law into a single statement. This law is written:
In this equation, P represents the pressure of the gas, V represents its volume, n represents the number of moles of gas, and T represents its absolute temperature. R is a constant called the universal gas constant. It has a value of 8.314 joules per kelvin per mole. According to the universal gas law, the pressure of a gas can be doubled in three ways: (1) the gas can be squeezed into one-half its original volume, (2) twice as much gas can be forced into the original volume, or (3) the absolute temperature can be doubled.