### what are chemical equations?

A chemical equation is a symbolic representation of a chemical reaction in terms of chemical formulas. An example of a chemical equation would be:

 2Na + Cl2 -> 2NaCl

example of chemical equation

This chemical equation would stand for the burning of sodium in chlorine to produce sodium chloride. The formulas on the left side of the equation would stand for the reactant. A reactant is the starting substance in a reaction. The arrow, ->, means either "yields" or "reacts to form." The formulas to the right of the arrow stand for the product formed in the chemical reaction. A product is the substance that results from a chemical reaction. The coefficient in front of the Na, 2, gives the number of molecules or formula units involved in the reaction. Coefficients of one are usually understood, so they are not written. Sometimes it helps to indicate the states or phases of the substances in a chemical reaction. We can do this by placing certain labels, which stand for the various phases, following the formula of a substance in a chemical equation. Here are the labels:

 (g)=gases (l)=liquid (s)=solid (aq)=aqueous solution

phase labels

When we use the labels which we have just learned our former equation becomes:

 2Na(s) + Cl2(g) -> 2NaCl(s)

example of chemical equation with correct phase labels

In a chemical equation we can also indicate the conditions under which the reaction takes place. If the reactants in the chemical reaction are heated, we indicate this with the Greek symbol delta, , over the arrow. Below is the equation that indicates that solid sodium nitrate, NaNO3 decomposes when heated to give us solid solium nitrite, which is NaNO2, and good ole oxygen, which is O2.

Oftentimes in chemical reactions there will be the addition of a catalyst. A catalyst speeds up a chemical reaction without being consumed in the overall reaction. Guess what, as you probably expected, there is a way to represent the addition of a catalyst to a chemical reaction. We do this by writing the catalyst involved in the reaction over the arrow. Here is an example, say that we have an aqueous solution of hydrogen peroxide, which is H2O2. When this solution of hydrogen peroxide is exposed to platinum metal (Pt), the hydrogen peroxide decomposes into water and oxygen gas. The platinum speeds up the reaction of the decomposition of H2O2 into H2O and O2 and acts as a catalyst in this reaction (you see, hydrogen peroxide gradually decomposes on its own over time). We would represent the equation below: