The object of this section is to show how the evaporation and condensation of water can put so much energy into a system. The math comes later, but first you need to understand a few terms.

Background:

The Table of Chemical Elements lists the elements in order by counting the number of Protons, called the atomic number. Hydrogen has 1, Nitrogen has 7, Oxygen, 8 and so on.

Most atoms have 1 or more Neutrons for each proton. The atomic weight of an atom is an average based on a large sample containing atoms with variations (called isotopes) in their neutron count. This is why atomic weights aren't exactly even numbers, such as Oxygen weighing 15.99994. For weather purposes, 16 is good enough.

A 19^th century scientist named Avogadro developed the idea the a unit of any element equal to the atomic weight has the same number of atoms as any other element's for it's atomic weight under the same conditions. This means a lot for anyone trying to compare energy in different substances, because it gives you a way to make sure you are dealing with the same number of particles in both samples.

The Mole:

As it turns out, if you take the atomic weight of any substance in grams (called gram atomic weight), you will always have 6.02 x 10²³ particles. This amount of mass is called a mole. The most interesting part for weather has to do with a mole of gas: at Standard Temperature (15°C) and Pressure (1013mb), the volume is 22.4 liters. Always. This works for any gas, including mixtures like the atmosphere! This means a known amount of water vapor can be directly measured for energy and energy changes.

Energy:

For purposes here, the easiest energy unit to use it the calorie - the amount needed to heat 1 gram of water 1°C. Since energy (and mass) cannot (normally) be created or destroyed, the calories going into heating or phase change come back out when the parcel is cooling. This release is a driving force in the atmosphere!

Consider the hapless Sci-Fi movie extra being zapped by a space alien ray gun. Based on the information above, we can calculate how much energy is involved. Let's start with an average 178 lb (81 kg) actor. Given that most of the human body is water, we can mostly ignore the hair, bones, vinyl shoes, velour shirt, and shocked look on the soon-to-be vaporized actor, and work strictly with the 81 kg number alone. Further, let's allow one full second for the alien ray gun to turn our non-Oscar nominated Thespian from flesh to dust. This breaks down as follows:

In other words, the one second given to evaporate the doomed crewman required over 225 Megawatts -- enough to power a Chicago suburb and then some. The ray gun generated over 300,000 horsepower in that one second, and the alien's arm (tentacle?) didn't get ripped off at the shoulder, either! Not only were the batteries really, really, good, but the gun was more than 99.99% efficent. Otherwise, the extra 200 kilowatts of waste heat would have fried them both anyway.

Speaking of vapor (water, that is), where did it go? Let's see: Allowing that real space alien ray guns don't destroy the matter they shoot (big, whopping, humongus numbers involved), then the water mass would occupy the space of our 81 kg target. By a wonderful concidence of the metric system, those 81 kg occupy exactly 81 liters of volume! (That's 3.8 liters/gallon and 1000 liters to the cubic meter, about 1.3 cubic yards.) The gram atomic weight of water is 18, based on one Oxygen = 16 and 2 Hydrogen at 1 each, so 16 + 1 + 1 = 18. This means a mole of water weighs 18 grams. OK, math time:

So even if the bones, hair, and artsy clothing promptly crumbled to dust, the 81 liters of water flashed into over 1,200 times it's volume turning the a human-sized actor into a hot-air-balloon sized bubble of steaming water vapor. Hollywood aside, if our space alien wasn't incinerated by the waste heat from it's own ray gun, the blast wave from the ex-actor target would have flattened it!

So What?

As ridiculous as the actor-goes-poof example is above, this is exactly how steam engines and thunderstorms produce energy. The example involved only one second, but the work produced by engines and storms can go on over hours. The conversion from Kilowatts/second and horsepower/second to /hour is by dividing by 3600 (60 minutes x 60 seconds). So the steam engine that boils 81 kg of water in an hour produces about 63 Kilowatt hours or 84 horsepower worth of steam. Much more realistic than the episode of "Star Bleep" above.

By comparison, a thunderstorm dropping one centimeter (1 inch = 2.54 cm, 1 cm = 0.01 m) of rain over one square kilometer in a hour works out like this:

As you can see, water condensation within a small thunderstorm casually dropping 1/3 inch of rain in an hour over a kilometer square releases nearly a million horsepower -- enough energy to power most of Chicago. For that matter, nimbostratus doing the same thing would involve the same amount of energy!

A real glutton for punishment could use the 10,000 tons of water to calculate exactly how many cubic kilometers of air passed through the LCL, CCL, or LFC based on the mixing ratio values for a storm of their own design. Suffice it to say that many dozens of cubic kilometers were lifted through the condensation level to produce the precipitation, and enormous amounts of energy were released in the process -- all because of latent heat.