Let us first look at some definitions:

An ATOM is the smallest particle of an element that retains the chemical properties of the element.

A COMPOUND is two or more atoms combined chemically in definite proportions such as H2O which always has two hydrogen atoms and one oxygen atom.

A MOLECULE is the smallest unit of a compound that retains the chemical characteristics of the compound.

A MIXTURE can be either homogeneous (same composition throughout) or heterogeneous (not the same composition throughout).

A SOLUTION is a homogeneous mixture of two or more substances with the substance present in the largest amount categorized as the solvent and the other(s) are called solutes. A solution of salt and water will always have water as the solvent because it is not possible to have such a solution with salt in the greater amount. However in a solution of water and ethanol, either on could possibly be the solvent.

PHYSICAL CHANGES are changes which do not change the atom ratios of the substance such as boiling and freezing.

CHEMICAL CHANGES are changes which do change the atom ratios of the substance and can create entirely new substances such as the burning of gasoline and the rusting of iron.

EXTENSIVE PROPERTIES are properties which depend upon the amount of matter present such as V, mass, and the number of moles.

INTENSIVE PROPERTIES are properties which do not depend upon the amount of matter present such as temperature and pressure.

Another way of looking at intensive and extensive properties is that intensive properties cannot be obtained by summing over all the values of that property over the entire system. For example we could measure the temperature at each spot in the room and we would then have a set of numbers [T1,T2,T3,.....Tn]. You know that the temperature of the room is NOT the sum of all of those numbers so temperature is an intensive variable. However we can do the same for volume -- measure the volume at each volume element of the room and set up the set of all volume elements [V1,V2,V3,.....Vn] -- and we know that the total volume of the room WOULD be the sum of all those volumes.

Matter is anything that occupies space and has mass. Consider that we have three containers of the same size and that we put the same number of molecules of some substance in each of the containers but in one container the molecules are in the gas state, in the second container the molecules are in the liquid state, and in the third container the molecules are in the solid state. A little thought tells us that the gas molecules will fill the container, the liquid molecules will all settle filling the bottom of their container, and the solid molecules will be clumped together at the bottom of the container.

From this thought experiment, we can see that the average distance between gas molecules is much greater than the average distance between liquid molecules which is greater than the average distance between solid molecules. Then we can say that the Vgas >> Vliquid > Vsolid. We will utilize this information a number of times throughout the semester.

Now take a practice quiz to help you understand if you understand the basic concepts.
You must use your real name when it asks for a name.
The test will only submit when you have answers all of the questions correctly.
If you are not taking this course for credit please do not answer all the questions correctly for I don't want to be flooded with email answers to the tests.

Web Author: Dr. Leon L. Combs
Copyright ©1999 by Dr. Leon L. Combs - ALL RIGHTS RESERVED