FREE ESSAY ON CHANGES OF PHASE

CHANGES OF PHASE

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.