Warning: math ahead. This is one of the very few times I'll post an equation. It gets a little hairy but it'll prove useful for the discussions of storms and other atmospheric goings-on.
The Ideal Gas Law is an equation of state variables--fundamental measurable aspects--of a hypothetical, "ideal" gas. It approximates the behavior of most gases fairly well, so it is used frequently throughout science to predict how a gaseous system will act. The equation is especially useful in rough, "first order of approximation" applications.
It was developed in 1834 by Benoit Paul Emile Clapeyron, who drew on the work of several others. The basic equation is this:
PV = nRT
Defining each variable:
P = pressure. Pressure is a measure of force exerted on an area. The metric (or Système Internationale, or SI) unit is the pascal (Pa), or more frequently the kilopascal (kPa). 1 kPa = 0.145 psi. One atmosphere of pressure = 14.7 psi = 101.3 kPa.
V = volume. Generally measured in cubic meters.
n = number of moles. A mole is a huge number, describing a set quantity of atoms or molecules. There are 6.23*1023 molecules per one mole of a substance, a number named in honor of Italian chemist Amedeo Avogadro. (The number is written in scientific notation, meaning multiply 6.23 by 10 to the 23rd power. You get 623 with 21 more zeroes following--huuuuuuuuuge.) This number was chosen carefully to equate atomic mass to grams. For example, one molecule of water has a mass of roughly 18 (16 (8P/8N) for oxygen plus 1x2 (1P) for hydrogen) atomic mass units (AMU), or daltons. (Electrons weigh very, very little compared to the nucleus.) One mole (mol) of water, via Avogadro's number, weighs 18 grams. So using molar masses, chemists can directly equate measurements of mass with numbers of atoms, a highly useful tool in studying chemical reactions.
R = the universal gas constant (a number obtained via experiments).
T = absolute temperature of the gas. 0 degrees Celsius is hardly the coldest a substance can be. It is theorized that the absolute coldest possible temperature is -273.15° C. (Oxygen becomes liquid at one atmosphere pressure around -183° C.) Absolute temperatures are measured in degrees Kelvin (° K). 0° K = absolute zero. 273.15° K = 0° C.
You (fortunately) don't need to work through many tortuous examples to understand the basic gist of this equation. Since we know that the gas constant R will not change, and assuming the amount of gas (n) doesn't either, we can look at the relationships between the three state variables: pressure, volume, and temperature. An increase in temperature (T), at constant volume (V), means the pressure (P) must also increase. If the pressure (P) decreases, and the volume (V) either stays the same or increases only slightly, then the temperature (T) must also decrease. These are two dynamics we will return to in the future.
Tomorrow: How a thunderstorm forms.
Thanks for bearing with me on this one. Be well!
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