Section 10.3 – the gas laws gas in babies that breastfeed


One of the first relationships to be studied with gases was how pressure impacted a gases volume. Robert Boyle did many famous experiments with gases. These experiments were based on the observation that gases are elastic. (They return to their original size and shape after being stretched or squeezed.) Boyle studied the elasticity of gases in a J-tube.

By adding mercury to the open end of the tube, he trapped a small volume of air in the sealed end. Boyle studied what happened to the volume of the gas in the sealed end of the tube as he added mercury to the open end. Boyle noticed that the product of the pressure times the volume for any measurement in this table was equal to the product of the pressure times the volume for any other measurement, within experimental error.

Calculate the pressure in atmospheres in a car engine at the end of the compression stroke. Assume that at the start of the stroke, the pressure of the mixture of gasoline and air in the cylinder is 740 torr and the volume of each cylinder is 250 mL. Assume that the volume of the cylinder is 20 mL at the end of the compression stroke.

The French physicist Guillaume Amontons built a thermometer (in the later part of the 1600s) based on the fact that the pressureof a gas is directly proportional to its temperature. The relationship between the pressure and the temperature of a gas is therefore known as Amontons’ law.

Amontons’ law explains why car manufacturers recommend adjusting the pressure of your tires before you start on a trip. The flexing of the tire as you drive inevitably raises the temperature of the air in the tire. When this happens, the pressure of the gas inside the tires increases.

In 1779 Joseph Lambert proposed a definition for absolute zero on the temperature scale that was based on the straight-line relationship between the temperature and pressure of a gas shown in the figure above. He defined absolute zero as the temperature at which the pressure of a gas becomes zero when a plot of pressure versus temperature for a gas is extrapolated. The pressure of a gas approaches zero when the temperature is about -270°C. When more accurate measurements are made, the pressure of a gas extrapolates to zero when the temperature is -273.15°C. Absolute zero on the Celsius scale is therefore -273.15°C.

In June 1783 the Montgolfier Brothers made the first public demonstration of a model hot-air balloon and September – in the presence of King Louis XIV and Marie Antoinette – they flew a balloon carrying a sheep, a duck and a cockerel to demonstrate that it was possible to survive in the sky. Some weeks later Pilatre de Rozier, a science teacher, and the Marquis d’Arlandes, an infantry officer, became the first human air travellers when, in a hot-air balloon, they flew for 9 km (5.5 m) over Paris.News of this remarkable achievement spread throughout France, and Jacques-Alexandre-Cesar Charles immediately tried to duplicate this performance. While working with balloons, Charles noticed that the volume of a gas was directly proportional to its temperature. This relationship between the temperature and volume of a gas became known as Charles’ law.

This graph also gives us another way to define absolute zero on the temperature scale. Absolute zero is the temperature at which the volume of a gas becomes zero when the a plot of the volume versus temperature for a gas are extrapolated. The value of absolute zero obtained by extrapolating the data is almost the same as the value derived from the graph of pressure versus temperature. Absolute zero can be defined as the temperature at which the pressure and the volume of a gas extrapolate to zero.

Joseph Louis Gay Lussac (1778-1850) was a French chemist and physicist who was known for his studies on the physical properties of gases. He was born in Saint Léonard and educated at the École Polytechnique and the École des Ponts et Chaussées in Paris. After holding several professorships he became professor of physics at the Sorbonne from 1808 to 1832.

In 1804 Gay Lussac made balloon ascensions to study magnetic forces and to observe the composition and temperature of the air at different altitudes. In 1809 he formulated a law of gases that is still associated with his name. Gay-Lussac’s law of combining volumes states that the volumes of the gases involved in a chemical reaction (both reactants and products) are in the ratio of small whole numbers. In connection with these studies he investigated, with German naturalist Baron Alexander von Humboldt, the composition of water and found it forms when two parts of hydrogen and one of oxygen unite.

One of the easiest ways to measure a gas is by volume (provided that we keep the temperature and pressure the same). In 1800 two English chemists, William Nicholson and Anthony Carlise had demonstrated that water could be decomposed by an electric current into two volumes of Hydrogen gas, and one volume of Oxygen — a simple whole number ratio of 2:1.

This observation – simple whole number combining ratios by volume – became known as the "Law of combining volumes". These results certainly suggested that the formulas for water might be H 2O, for ammonia NH 3, and for Nitrogen dioxide NO 2.

Lorenzo Romano Amedeo Carlo Avogadro di Quareqa e di Carreto – Avogadro for short – was born in Turin, Italy in 1776, into a family of church lawyers. He too studied ecclesiastical law, earning his Bachelor’s degree at the age of 16, and a Doctorate by 20. After three years he decided that a career in law was not to his bent, and he began to study science and mathematics in earnest. In 1809 he was appointed professor of Natural Philosopy at the Royal College of Vercelli in isolated Northern Italy. In 1811 he proposed his now famous hypothesis that equal volumes of gases, at the same temperature and pressure, contain equal numbers of molecules.