the escape velocity. Almost all of the molecules in the atmosphere are below this velocity because of the temperature of the planet Earth (higher temperature = faster molecules).
Almost all? Yes. Earth is very slowly losing its atmospheric gases. The lightest ones go first—about three kilograms of H2 escape the gravitational pull of Earth per year. A few particles can escape because kinetic energy of gases is a Boltzmann distribution, and in a Boltzmann distribution there are always very small probabilities of very high values.
What is the composition of air?
Earth’s atmosphere is made up of 78% nitrogen (N2) and 21% oxygen (O2), if you ignore water vapor, which shifts too much to include in averages for the entire planet. The last 1% is made up of mostly argon (Ar), followed by carbon dioxide (CO2) and other trace gases.
What gives a substance its color?
The color of a substance is the combination of the light that is reflected back at your eye. In other words, you’re seeing the light that is not absorbed by the substance. Certain frequencies can be absorbed because of the electronic structure of a substance, while others simply bounce off back into your eye.
What is a glass?
A glass is a noncrystalline solid—it lacks order in the solid state. In polymer chemistry, scientists are concerned with the glass transition temperature (Tg), which is the temperature at which a material changes from a hard to a rubbery state. What’s neat about this transition is that the material is not changing phases (i.e., from solid to liquid), but is changing from one type of solid to another.
What makes mercury so dangerous?
Mercury can be absorbed through the skin, making it particularly dangerous to handle. Organometallic mercury compounds, like dimethylmercury (CH3HgCH3), are particularly dangerous and have caused the deaths of a number of laboratory research chemists. Most research on this most toxic of mercury compounds has ceased. Be careful cleaning up that broken thermometer!
What is a vacuum?
A vacuum is space without matter. The word vacuum derives from a Latin word that means “empty.” A perfect vacuum, or one with absolutely no matter in a given space, is very hard to achieve, but through modern engineering scientists can get pretty close without having to go into deep space to run their experiments.
Can sound move through a vacuum?
No. Sound is a mechanical wave, which means that for the wave to move, actual molecules must bump into one another. In a vacuum, there is no matter, so in space, no one can hear you scream.
How does a vacuum cleaner work?
We commonly use the word vacuum to refer to any area that is of relatively low pressure. The air in areas of higher pressure will spontaneously move into areas of lower pressure, and this is the principle upon which a vacuum cleaner operates. A fan is used to push air out of the vacuum cleaner, creating an area of lower pressure behind the fan. Air from the outside then comes rushing in to reduce the gradient in pressure, carrying dust and dirt along with it. Since the fan is running continuously, the gradient in pressure is constantly being maintained, so the vacuum cleaner is able to keep running even though air is always flowing in.
Can light move through a vacuum?
Yes. Unlike sound, light is an electromagnetic wave, so no molecules are needed to propagate the wave. But you knew this—the Sun’s light crosses the vacuum of space to reach Earth each and every day.
What are some chemical reactions that we can observe with our naked eye?
There are lots of chemical reactions that we can easily detect by sight. Some examples are the formation of rust on metal, wood burning, fireworks exploding, silver becoming tarnished, or baking soda and vinegar reacting with one another.
What makes paper towels absorbent?
Paper towels are composed of cellulose fibers, which are polymers that contain many sugar monomers. These sugar monomers can interact strongly with water molecules, which is what makes paper towels so useful for cleaning up when something gets spilled.
What is an electric current?
Electric currents are the flow of electrons through a material. The electricity that comes out of the wall in your home or office is just the flow of electrons through a wire.
An explosion is a dramatic example of a chemical reaction we can see with our naked eyes.
What makes a material a good conductor of electricity?
Materials that are good conductors of electricity have many “free” electrons. Here we mean free in the sense that they are not bound strongly to a given atom or molecule. Metals are often good conductors of electricity. Whether or not a material has freely conducting electrons is related to the detailed electronic structure of the material, and a thorough description would be beyond the scope of this book. Basically, the more electrons that are free to move around in a material, the more easily it can carry current, and the higher its conductivity.
What makes a rubber band stretchy?
Rubber bands are made of long polymer molecules. These are all tangled together, and you could think of them as being similar to a bunch of interwoven springs. The polymers can be stretched to a more extended state, which is what allows a rubber band to stretch without breaking. More accessible configurations exist, however, when they are in a more contracted state, which means that the more contracted states have higher entropy (see “Physical and Theoretical Chemistry”) and for this reason are more favorable. This is what makes the rubber band want to contract and is what gives rise to its elasticity. (Check out “Polymer Chemistry” for more questions on polymers.)
How are soft drinks carbonated?
Soft drinks are carbonated using pressurized CO2 gas and a siphon that introduces the pressurized gas into the water or soda. The CO2 gas is forced into the liquid at a concentration beyond that which could exist under atmospheric conditions and then the container is sealed, preventing it from being released. That’s why if you leave a glass of soda sitting out, it will go flat; the CO2 escapes into the air.
Why might a soft drink freeze when you open it?
Remember that the freezing point of a solution is decreased by having anything dissolved in it. When a soft drink is opened and CO2 rushes out, less CO2 is present in the solution, causing the freezing point of the solution to increase. So at a constant temperature, the increase in freezing point causes the soda to freeze. If you haven’t seen this happen, you can try to make it happen by placing a soda in the freezer for a while, but be careful not to leave it in too long or it might explode!
