[derbygirl2005]

   hi.  I need help in stoichiometry. My teacher isnt that great of a teacher, so i really didnt understand anything from him. Please help me in getting the key facts of it. I even had another teacher try to help me, it really didn't work either. PLEASE.

[Mitch]

Have you learned Algebra?

The key thing is to make sure the total number of atoms on the left hand side of a chemical equation equals the number of atoms on the right hand side of the equation. In order to do this, you can multiply any of the formulas by any number you want to in order to achieve this balance.

[derbygirl2005]

yes i learned algebra. but i just dont get the whole entire moles & molarity thingy (which was the previous chapter that we did and i didnt get it)

[jdurg]

One way to think of moles is as a counting unit.  For example, when you go and buy doughnuts, you generally say "I'd like a dozen doughnuts," not "I'd like 12 doughnuts."  With moles, you'd say "I need a mole of carbon," not "I need 6.022x10²³ atoms of carbon."  Molarity is simply moles in a liter of solution.  So if you have a one molar solution of hydrochloric acid, it means that in one liter of the acid, you have one mole, or 6.022x10²³ molecules, of HCl.  When looking at chemical equations, they are generally written in terms of molar quantities.  (Though when you're first learning them they try and teach you to have whole numbers in front of each molecule/atom, thus representing the reaction on a molecular scale).  But in the following equation, the whole numbers equal moles of the following molecule.

2H₂(g) + O₂(g) -> 2H₂O(g)

So we have two moles, or 2(6.022x10²³) molecules, of hydrogen gas reacting with one mole, or 6.022x10²³ molecules, of oxygen gas to create 2 moles, or 2(6.022x10²³) molecules, of gaseous water.  Does that make a little more sense now?

[derbygirl2005]

sortof. man. i wish that you were my teacher. maybe i get actualy get this crap.

[jdurg]

Another thing to remember about moles is the relationship between the atomic mass of an element and the molar mass of it.  One mole of an element is equal to it's atomic mass, but in grams.  For example; carbon has an atomic mass of about 12.011 AMU.  Therefore it's molar mass, or the mass of one mole of carbon atoms, is equal to 12.011 grams.  Knowing this relationship is crucial to figuring out stoichiometry problems since many times those problems aren't in whole moles.  So if you had a problem which asked you to figure out how many grams of carbon you'd get from a reaction that produces 0.367 moles of carbon, you'd simply have to take 0.367 and multiply it by the mass of one mole of carbon (12.011 grams).  

[estranged]

its my first post in this forum...n00b   um....
I would like just to say a h.u.g.e. THANK U!!!!