I Used to Know That_ Stuff You Forgot From School - Caroline Taggart [28]
☞ OXIDATION
Oxidation is a commonly quoted chemical reaction, and the most common example of it is rust. In fact, anything that reacts when it comes into contact with oxygen is being subjected to oxidation: The green coating on an old copper coin is the result of oxidation; the browning of fruit is caused by oxygen burning away at the stuff that is released when you peel off the protective skin. Rust is, strictly speaking, the oxide that forms on iron or steel. Stainless steel doesn’t rust, because it is protected by a layer of chromium, which doesn’t react to oxygen in the same way.
☞ DIFFUSION AND OSMOSIS
Molecules are constantly in motion and tend to move from regions where they are in higher concentration to regions where they are less concentrated—a process known as diffusion. Diffusion can occur in gases, in liquids, or through solids.
Osmosis is a form of diffusion that is specific to the movement of water. Water moves through a selectively permeable membrane (that is, one that lets some types of molecules through but not others) from a place where there is a higher concentration of water to one where it is lower.
In any form of diffusion, when the molecules are evenly distributed throughout a space, they have reached equilibrium.
☞ BOILING AND FREEZING POINTS
If the temperature is low enough, every known substance except helium becomes a solid. The temperature at which this happens is called its freezing point. Above its freezing point a substance is a liquid. At the other end of the scale, if the temperature is high enough, it becomes a gas, and this is called the boiling point.
Solid is the only state in which a substance retains its shape; a liquid assumes the shape of its container but does not necessarily fill it; a gas expands to fill the space available.
Take water, for instance. In its solid state, it is ice and retains its shape—whether ice cube, icicle, or iceberg—until the temperature rises sufficiently for it to melt and become liquid (water). If you take a tray of melted ice cubes and pour the water into a pan, it will take the shape of the container—that is, spread out to cover the bottom—but it may only come a certain distance up the side. If, however, you then turn on the heat under the pan, put a lid on it, and boil the water, it will turn into gas (steam), fill the pan completely, and probably seep out under the lid as well.
Nonscientists commonly measure temperature according to one of two scales: Celsius and Fahrenheit, both named after the people who invented them. Celsius was also once called centigrade, from the Latin for one hundred degrees.
The freezing point of water is 0°C, and its boiling point is 100°C. The equivalent in Fahrenheit is 32°F and 212°F. This means that the difference between freezing and boiling is 100°C and 180°F (212 - 32).
To convert Celsius to Fahrenheit, you need to divide by 100 and multiply by 180, which can also be expressed as multiplying by 1.8, or . Then, because the freezing point of water is 32°F, not 0°F, you need to add 32:
15°C x 1.8 = 27; 27 + 32 = 59°F.
To reverse the process, first deduct 32 from your Fahrenheit temperature, then divide by (or multiply by ; it’s the same thing):
104°F - 32 = 72; 72 x = 40°C.
This works for any temperature above freezing.
There are two other scales used by scientists—the Réaumur and the Kelvin. According to René Antoine Ferchault de Réaumur, water freezes at 0° and boils at 80°. Kelvin is interesting because he invented the concept of absolute zero, a temperature at which particles cease to have any energy—so a scientific impossibility, although in the laboratory, scientists have achieved temperatures within a millionth of a degree of it. Absolute zero is 0°K, or -273.15°C, which is very, very cold. Imagine how much energy you would have at that temperature.
Physics
Physics deals with the properties and interactions of matter and energy, but its theories are constantly being redefined as physicists discover new