Look up the atomic mass units of a typical molecule, say O2. Monoatomic oxygen is very rare in nature, like H2, N2, these elements usually occur in pairs, molecules of 2.

You can look up the atomic mass of oxygen in the periodic table. The atomic mass units (amu) of oxygen is 16, it is the sum of the protons and neutrons in the nucleus. electrons are so light they don’t really matter. Since O2 can’t stand to be alone, the O2 molecule masses 32 amu.. Each carbon atom weighs 12 amu. So the CO2 molecule masses 12+32 amu or 44 amu.

As you can imagine, an amu is an extremely tiny number, very cumbersome to work with, so chemists have come up with a really clever trick to simplify their calculations of chemicals involved in reactions. They have invented the concept of the mole, which is short for gram-molecular weight. A mole of a molecule (or atom) is
the amount of that molecule or atom in grams where the number of grams equals the number of amus. So a mole of carbon is 12 grams, A mole of oxygen is 16 grams, and a mole of O2 is 32 grams. So a mole of CO2 weighs 12+16+16 = 44 grams. One mole of carbon burned in a mole of pure O2 will yield 1 mole of CO2.

Now at shirt-sleeve temperatures and pressures, carbon is a solid and there is no easy way to calculate how much space it takes up. You have to look it up. But O2 and CO2 are gases, and all gases take pretty much the same volume at the same temperature and pressure. At Standard Temperature and Pressure (STP) a mole of any gas takes up about 22.4 liters of volume. STP is defined as 1 atmosphere pressure at O degrees Centigrade. It varies slightly from gas to gas, due to differing attractive forces between molecules, but the volume of a mole of any gas at STP is usually pretty close to 22.4 l. And it turns out that 1 mole of any element or compound contains 6.02 x 10^23 particles. You may recognize this as “Avogadro’s Number”. So if you burn a mole of carbon 6.02×10^23 atoms, or 12 grams, in pure oxygen gas, you will wind up with 1 mole of CO2, and some left-over O2. 1 mole of O2 molecules (two moles of oxygen atoms) will oxidize the carbon. The CO2 will be mixed up with the left-over oxygen.

I know its simple, and I know most of you have been exposed to this, but it represents an astonishing achievement of the human intellect. I had a devil of a time understanding it myself as a student in high school. But once it sank in, I realized what an incredible stroke of genius it represents, an understanding of the atomic structure of matter, derived simply by conducting a few experiments and making a few simple measurements with apparatus you could find in any kitchen.

I salute Dottore Amedeo Avogadro, and my teacher, Mrs Hernandez, for showing me how the universe is put together at the atomic level.

1776-1856

And one more thing, this man was born in the same year as our country. As far as history is concerned, it wasn’t all that long ago. We’ve come a long way in a very short time.