|
|
|
|
|
|
|
|
|
|
|
|
Only $12.95 / Page!
|
|
|
|
|
|
Order your custom written essay today for a half-price. Our best quality
essays are available from $12.95 per page! |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
To define matter, one would say that it is something that occupies space and has weight.
Matter naturally occurs in three phases: solid, liquid, and gas. Changing from a solid to a
liquid, liquid to gas, etc. can be referred to as a change of state. Changes of state (or
phase) effect our everyday lives. This chapter on changes of phase should actually be
called Energy Transfer. The whole basis on changing a substance's state is that it is using
energy to get from one state to another. To understand the real difference in the phases
of matter, you must understand the difference in the energy of the phases. Energy is found
inside matter. You can think of this energy as the motion of the particles making up the
matter. As the energy increases inside matter, the particles move faster and faster.
Phase changes are a type of physical change. They require energy (in this case heat
energy) to either be removed or added on to the substance. On earth, three main types of
phases. These are: solids, liquids, and gases. The fourth phase is called plasma and the fifth
which scientist are researching and building models of is super-solids. The solid state is
when a substance's inner particles are not free to move around, but can vibrate. The liquid
state is when a substance's inner particles become a bit loose, and they are free to move
around. They aren't completely free, but have the ability to take the volume/shape of their
container. In the gas state, the particles are free to move, and can take the form of and fill
the container they are put in.
Evaporation is the gradual change of a liquid to a gas without boiling. The factors
that influence evaporation are temperature, solar energy/sunlight, low humidity, or
saturation level or the air. The temperature simply represents the average kinetic energy of
the molecules in a substance.
Molecules are constantly in motion, whether their speeds are fast or slow; they are
never standing still. Their speeds mainly are dependent on the temperature of the liquid.
At rapid speeds, (and high temperature) the molecules tend to bump each other, due to
the molecular forces that are acting upon them. While bumping into each other, kinetic
energy is either being gained or lost. Those molecules that have gained kinetic energy are
being pushed up from below, and this is the point where it may be possible for them to
escape the surface of the liquid. In addition, they have to overcome the attractive forces
pushing them downward. Because few molecules are able to attain this status, few escape.
This is the main reason why evaporation of a liquid is such a slow process, and it also
explains why evaporation is referred to as a cooling process. Such is used even in the
human body, where sweat glands cause a heated body to perspire to maintain body
temperature.
The molecules that are not able to escape the surface are left in the liquid,
therefore cooling the liquid because the molecules contain a lower velocity (they aren't
moving as fast).
Amazingly enough, there is a process that reverses the effect of evaporation. This
is called condensation, which is when a gas changes to a liquid. Condensation is a cooling
process. Taking away the heat shrinks the volume of the vapor and lowers the velocity of
the molecules, plus the distance between them. The loss of energy will cause the
transformation of the gas into a liquid. Basically, there are molecules in the air that want
to become a liquid, and the opposite of evaporation occurs. They are attracted to the
liquid, and once they get close enough to it, or get enough kinetic energy to get near it,
they may strike it. At this point, the molecule has just slammed into other molecules and it
has lost it's kinetic energy. Now, even if it wanted to escape, it would have to gain way
too much energy. So it is stuck in the liquid, and is now a part of it.
There are always different levels of water vapor in the air. The relative humidity
compares the temperature with how much water is in the air. When the air is holding as
much vapor as it can, the most before it turns into a liquid, it is referred to as being
saturated, or at 100% humidity. This also happens when there is an equilibrium (an equal
amount of water molecules are being evaporated and condensed). This ultimately happens
when the slower molecules in the air tend to stick to each other and form a liquid-like
vapor in the air. It can occur in low or high temperatures.
In this same case, if the larger particles condense, it has just made a cloud or fog.
Fog is the same thing as a cloud, except fog occurs near the surface of the earth while a
cloud occurs in higher elevation. They form when air cools and is unable to contain as
much water vapor. The condensation and cooling of the air causes them to happen . So
what happens if there gets to be too much water vapor, that the air can't hold it all? The
droplets would stick to each other and cause what we know as rain. *
Evaporation and condensation are relatively slow processes. This is due to the fact
that it takes a lot of energy for just one molecule to escape the state that it's in to become
another . Different situations make substances evaporate and condense at varying rates.
So if you leave a glass of water out for a few days and the water level doesn't
change, does that mean that evaporation and condensation didn't occur? Not at all! What
has occurred is called an equilibrium. This happens when the liquid evaporates and
condenses at the same rate.
If the air doesn't contain much water, evaporation will occur a lot quicker than
condensation will. In air where there is a lot of water, evaporation will happen only a little
faster than condensation. On dry summer days it is possible to stay reasonably comfortable
even though the temperature is fairly hot . The reason is that our bodies perspire, cooling
us off. We may not even know that we are perspiring because it evaporates so fast off of
the skin that we don't even notice. On the other hand, on humid days the evaporation rate
is so slow that we constantly feel sticky and wet. Water vapor in the air effects the
evaporation and condensation rates.
Water boils at 100* Celsius, and despite popular belief it is actually a cooling
process. Water is being cooled by boiling as fast as it is being heated by energy from the
heat source. When the heat source warms the pot of water, the heat turns the water
closest to it into a gas. The gas molecules are, at this point, moving faster than that of the
liquid. The gas will want to get to the surface of the liquid so it can escape, and it will
push it's way through the liquid to get to the surface. This is why boiling water bubbles!
One major factor of boiling water is that it all depends on the atmospheric
pressure. An example of the role that pressure has on the boiling point would be found at
sea level. Boiling point would be at about 97* C rather than 100* C, because the vapor
pressure cannot exceed the atmospheric pressure . In addition, if water is already boiling,
it will remain at a constant temperature. Even if more and more heat is added, it will not
fluctuate it's temperature.
The Gas Laws:
Boyle's Law -
· The volume of a fixed amount of gas varies inversely with the pressure of the gas.
· As pressure increases, volume decreases.
· As pressure decreases, volume increases.
Charles' Law -
· The volume of a fixed amount of gas varies directly with the temperature of the
gas.
· As temperature increases, volume increases.
· As temperature decreases, volume decreases.
Word Count: 1353
|
|
|
|
|
|
|
|
|
|
|
|
|
