Purpose

Stoiciometery is quite simply the mathematical convertion of units to acheive a dersired units in the result. This is a major concern in chemistry because chemists are constantly using different types of measurements to measure the same substance. Stoichiometry is also far more reaching than normal dimensional analysis. It reaches into almost every mathmatical equation that relates to chemistry. This is because most equations simply describe relationships between certain properties of a chemical. Since most properties have their own unique unit, it becomes imperative to create some mathimatical link between them. Often times this relationship will not be linear, so equations may look like they are expressing something very complex; however, it is usually still all based on defining a relationship between properties.

What is a Mole?

Most of the units and their conversions should be something with which you are already familiar. But one new unit which may be new is a mole. A mole is simply a quantity, 6.022*10²⁴. Every time you see the word mole, it simply refers to 6.022*10²⁴ of something. Usually it will refer to the number of moluces in a substance.

This is one of the most important units in chemistry. With a little help it establishes the basis for predicting amounts of products and rates of reactions. Its claim to fame is that it is the number of atoms in one gram of hydrogen. Through experimenation scientist have determined what the mass of one mole of each element on the Periodic Table. This number is listed as either the atomic mass or the molar mass of an element.

This means that everytime you are given the mass of a certain chemical in a certain reaction, then it is possible the exact number of atoms involved in the reaction. Before there was the mole there was no way of telling how many atoms were going to react.

Methods and Examples

Stoichiometric setups are often displayed in a chart format with every column being a fraction which is usually taken form conversion tables. Here is a simple one which is converting 3 inches into the equivical number of centimeters:

The purpose of the chart is to make sure that for ever unit that is on top, there is the same unit on the bottom except for the unit of the final answer. It is recommended that in the beginning, you should cross off the units as you eliminate them:

Now all that's left is to mutiply all of the top together and all of the bottom together. Now divide the top by the bottom and there is the final answer.