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This is a combustion reaction of methane that is often seen in chemistry classes. [Figure1]

Chemistry is going on everywhere and all the time. It's in the trees, in the clouds and anything you can think about. There are so many chemical reactions (like the one above for example) that there has to be a standardized way of denoting which of the millions of reactions you are talking about. And there is!

Word Equations

The reaction of the Bunsen burner, above, can be described in this way: Methane burns in the presence of oxygen to form carbon dioxide and water. This is very long for such a simple reaction. Just imagine if this was done for a much longer and complex reaction, such as the formation of proteins in the human body; It would be a paragraph long!  To make it shorter and easier to understand this can be done with the above reaction:

Methane + Oxygen \rightarrow Carbon dioxide + Water
NOTE: The convention is to write these in Reactants (separated with a plus) \rightarrow Products (separated with a plus)

Now try to make a Word Equation for this: When solid silver metal is exposed to sulfur, sulfer sulfide is produced.

You can find the answer here.

Chemical Equations

Writing all of that out can be tiresome and tedious especiallyin longer, more complex reactions. Word equations don't give the need information of the chemicals that are being used either. Thankfully, there is another easier and, in someways, a better way.

Chemical equations use the chemical symbols of the substances used. For example, the reaction above used sulfur whose symbol is "S". Chemical equations show the chemical make up of the substance, rather than just the name of it like a word equation. Chemical equations also make a depiction of a chemical reaction smaller and quicker to understand. Unbalanced chemical equations are called skeleton equations.

The skeleton equation for the Bunsen burner would be: CH4(g) + O2(g) \rightarrow CO2(g)+ H2O(g)

Remember: The writing convention is the same for both equations, the first letter of any chemical symbol for any element is capitalized, the number to show how many of an element is in the compound is subscripted, and the phase type is in parenthesis.

Knowing what each symbol in the equation means is important. Describe what each symbol means in the table below.

Symbol  The Description for the Symbol
+
\rightarrow

\rightleftarrows

(s)
(l)
(g)
(aq)
\overset{Pt}{\rightarrow}
\overset{\Delta}{\rightarrow}

The answer to the table can be found here

Balancing Chemical Equations

Even though the skeleton equation tells us the amount of and what atoms are in the compound, it still does not follow the law of conservation of mass. As you can see, there are only two hydrogen atoms on the right of the skeleton equation for the burning of methane but there are four on the right. But since matter cannot be made, how did it get there?

In order to follow the law, we must balance the equation, meaning we must have the same amount of one atom on both sides. 

The balanced equation for the burning of methane is: CH4(g) + 2O2(g) \rightarrow CO2(g)+ 2H2O(g)

Remember: To balance the equation, you must add coefficients to depict the number of molecules that will be used.
In this case one molecule of methane reacts with two molecules of oxygen gas (diatomic) and yields one molecule of carbon dioxide and two molecules of water. 

Lets try to put all three of these topics together. Try to write the final balanced equation for: Carbon reacts with hydrogen to form methane.

The balanced equation can be found here.

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