Introduction to Gas Laws
B. A. Rowland
Phases of Matter
There are three distinct phases of matter that we can observe on the Earth: solids, liquids, and
gases. There are also two others: plasmas (ionized matter—very hot!) and Bose-Einstein
condensates (when all atoms are behaving as an entire quantum system—very cold!). We will
only focus on gases (this lecture) and solids and liquids (later in the course—these are known as
the condensed phases of matter). Every bit of matter known has a preferred state of matter at a
given temperature and pressure. You can change the state of matter for a substance by changing
the temperature and/or the pressure (think condensation, evaporation, sublimation, etc). Solids
are regularly ordered and have high intermolecular forces, liquids are semi-randomly ordered
and have moderate intermolecular forces, and gases are completely chaotic and for some cases
the intermolecular forces between particles can be ignored. Since gases are the focus of study, it
is important that we define the variables we will be using to characterize gases:
is the pressure
(arises from the collisions of gas molecules with the walls of the container),
is the volume (the
amount of space occupied by the gas),
is the number of moles (how much gas you have), and
is the temperature (a measure of the average kinetic energy of the particles comprising
Important Dates in the History of Gases
Air is theorized to be one of the four fundamental elements.
Van Helmont: discovers carbon dioxide through a chemical reaction. Finds that although
carbon dioxide does behave like “air”, it has some very different properties as well (early
designed the first barometer, a pressure measuring device, circa 1643.
invents the vacuum pump, circa 1654.
first to quantitatively study gases, proposes Boyle’s law (late 1600s).
Lavoisier, Priestly, and Scheele:
co-discoverers of oxygen, 1770s.
first solo balloon flight (he used hydrogen) and Charles’ Law, 1787.
Proposes Gay-Lussac’s law, 1802.
Composition of atmosphere is uniform, 1805.
Proposes Avogadro’s number, in 1811.
Pressure in physics is defined as force per unit area. Mathematically, that is