Don't be afraid of that word quantitative.
In our third class, we will start by look at the practical consequences of the fact that atoms all have different weights, but react with each other in simple ratios of atoms (which are hard to count), and not so simple ratios of masses (weights, more or less). We'll start with the very simple reaction discussed on the Class #2 page (hydrogen reacting with oxygen to give water).
Please review that material at the Class #2 page.
Then we will look one or two more complicated reactions.
Finally, we will ask, "What determines the formulas of compounds? Why NaCl, but MgCl2?"
Balanced Chemical Equations
Based on the discussion of the reaction of hydrogen gas with oxygen gas (see Class #2 page), see if you can balance this equation for the complete combustion of ethanol (aka ethyl alcohol).
The heat released by this reaction is called its heat of combustion. Reactions can entail either the absorption of heat or its release. Burning ethanol produces, or releases, heat. Can you think of any processes that absorb heat? When such a process occurs, its container or its surroundings get colder, because it is absorbing heat from the surroundings. Hint: such a process occurs on your tongue when you eat a donut covered with confectioners sugar. We might take this matter up later in a unit on chemical thermodynamics, which quantifies energy changes during chemical processes. Bet you can't wait.
You will learn in class that LOTS of things are going on when a candle burns. There is even more to learn, if you are interested. Back in 1825, the brilliant British scientist Michael Faraday (best known for pioneering work in electricity and magnetism) inaugurated the Royal Institution Christmas Lectures, with a program for children called "The Chemical History of a Candle". His lectures are preserved in the book, still in print, and now in the public domain, Chemical History of a Candle, by Michael Faraday.
The lecture series goes on today, and has seen many celebrated scientists at the podium (full listing HERE). The lectures have been televised since the mid-'60s (many available on Youtube), and still are aimed at general audiences, especially young people. With typical British urgency in matters of diversity, the first woman to preside was Susan Greenfield in 1994, a mere 169 years after the series began. In the 42 years since, seven or so more women have been honored to lecture. British science organizations have been characterized as stuffy clubs for old boys, but I can't imagine why, can you?
Why do atoms combine as they do?
Why NaCl but MgCl2?
It has to do with periodicity! The chemically prudish non-reactivity of the noble gases suggested that certain "magic numbers" in the outer shells (2, 8, 8, 18... the widths of the rows or periods) confer particular stability on structures whose atoms hold or share electrons in those numbers. We will look at very simple models that allow prediction of chemical formulas involving two or more elements.
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* Here's the balanced equation for ethanol combustion
