Post 1 Stoichiometry

Stoichiometry is our next unity that involves finding the relationships, measurements, between reactants and products within a chemical reaction. It begins with balancing the equation, finding the molar mass of the reactant then converted to mols, using the coefficients (mols) of the reactant to the converted product, and then converting the mols of the new product back to mass (grams).
 
Using this same method, you can use stoichiometry to find the limiting reagent within a  reaction by calculating each of the reactants using the same conversion method as described above, converting it into the product, and then finding which produces the least amount of product using the given mass. This is the LR which can only produce so much of the product leaving the other reactant with excess.

When determining the excess reactants left over, use the amount of product created with the limiting reactant and convert it using the same formula as stated before into the excess reactant to find how much of that element (species) was used up in the chemical reaction. Then subtract this answer from the original mass of that reactant that you began with to find how much was not used in the reaction (or left over). This is your excess.

Finally, stoichiometry is also used with the chemical equation Yield% = 100X(actual yield/theoretical yield)

When doing all of these formulas, make sure the equation is balanced and the only transition of elements can be calculated through mols.

Here's some sites that may help.
khanacademy
CrashCourse
chemwiki 
chemteam