MHS Chemistry
Physical and Chemical Changes

Physical Changes are changes that result in a new appearance for the same material. They include changes such as ripping, crushing, folding, and shattering, as well as any changes of phase or state, and the formation of mixtures (including solutions). They are relatively easy to reverse.

The states of matter are solid, liquid, gas and plasma. Most of us are familiar with the first three states, but plasma is less common. In chemistry, plasma is that state of matter in which many or all the electrons have been stripped from the atoms. It is a very hot gas, and is found in the atmospheres of stars, around lightning bolts, and two other very common places. Fluorescent lights work by making a gas into plasma, then letting the electrons back on (this is when they give off light). So fluorescent lights in the US contain plasma 60 times a second as long as they are on. The other place one can find plasma is in a fire: look very closely in a candle flame, and the "empty" space between the wick and the flame is where the plasma is. The part of the flame you can actually see is the part that just got it's electrons back (in the new arrangement of atoms), and so is no longer plasma.

 
Changes of State
from -------->
to:
solid
liquid
gas
plasma
solid
x
fusion,
freezing
condensation
-
liquid
melting
x
condensation
-
gas
sublimation
evaporation,
vaporization,
boiling
x
condensation
plasma
ionization
ionization
ionization
x

A phase of matter is different from a state of matter (it is common but incorrect to use these terms interchangeably). A phase of matter is a part of a substance with distinct properties. Think of it this way: oil and water don't mix, so putting them in the same container gives one state (liquid), but two phases (two distinct regions of the liquid).

Chemical changes occur when a process results in a new substance being formed with new properties. These are often accompanied by changes in color and/or temperature. They are also more difficult to imagine being reversed. Examples of chemical changes include cooking, digestion, and burning.

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