STOICHIOMETRY

STOICHIOMETRY!!!! 

(Like seriously, I could not pronounce this word at the beginning...)



Anywayyyyy WHAT does this weird word actaully mean???
Well, we all know that "metry"means measurement right?? (if not, well now you know)
And "stoichio" means element in Greek! 
So PUT IT ALL TOGETHER, you get....the measurments of elements!!!! That's what Stoichiometry means. :)

- Stoichiometry is all about the quantities of the substance that are produced by chemical reactions.
- It shows the quantitive relationship with the products and the reactants in a chemical reaction.

For example: 

4NH3 + 5O2 ---> 6H2O + 4NO

= 4 molecules of NH3/moles react with 5 molecules of 02/mole of 02 to produce 6 molecules of H2O/moles of H20 and 4 molecules of NO/moles of NO

SOOO...
The first step in solving stoichiometry problems is to BALANCE THE CHEMICAL EQUATION!!
- That is very important beause the coefficients tells us the ratio of the moles and molecules in the equation.
- And remember to always include the units! Otherwise you might get confused later on in your calculations. It's only for your own good. :)

Example!!!

P4 + 5O2 ---> 2P2O5

How many moles P2O will be formed when there is 7.40 moles of P4?

7.40 P4 X 2mol P2O5/mol P4 = 14.8 mol P2O5

There will be 14.8 mol of P2O5!

Now that we got the basics, let's add in some MOLARITY!!! 


haha it's a mole!

So let's review theee formulas,

Molarity = mol/L
Litres = mol/M
mol = L X M



Example 1:

2 FeCl3(aq) + 3MgSCN2(aq) ---> 2Fe(SCN)3(s) + 3 MgCl2(aq)

How many moles of MgCl2 would be formed if 50.0 mL of 0.200 M FeCl3 is reacted with sufficient MG(SCN)2?

convert 50.0 mL into L which = 0.05 L

mol = (0.05 L)(0.200 M)
      = 0.01 mol FeCl3 X 3 mol MgCl2/2mol FeCl3 
      = 0.015 mol MgCl2

There will be 0.015 mol MgCl2.

Example 2:

2 FeCl3(aq) + 3MgSCN2(aq) ---> 2Fe(SCN)3(s) + 3 MgCl2(aq)

100.0 mL of Mg(SCN)2 is reacted with FeCl3 to produce 11.5 grams of Fe(SCN)3. What is the molarity of the Mg(SCN)2 solution??

11.5g Fe(SCN)3 X 1 mol Fe(SCN)3/230.1g Fe(SCN)3 X 3 mol Mg(SCN)2/2 mol Fe(SCN)3 x 1 mol/0.100L = 0.750 M

There is 0.750 M.

Example 3:

1Zn(s) + 2HCl(aq) ---> 1ZnCl2(aq) + 1H2(g)

At STP, what colume of H2 gas would be produced from 21.2g of HCl?

OMGG STP!!!! lets refress our memories, STP is 22.4L!

21.2 of HCl X 1 mol/36.5g HCl = 0.581 mol HCl X 1H2/2 HCl = 0.290 mol H2 X 22.4 L/1mol = 6.51 L H2

There will be 6.51 L H2




And that's it for STOICHIOMETRY! :D If you want more practice, here is a good website to check out!http://www.sciencebugz.com/chemistry/chprbstoich.html