Chem Class- January 20, 2010

We got a new booklet today called "Gravimetric Stoichiometry".

Then, we learned the following points that have to do with Stoichiometry:

• Coefficients in balanced equations represent moles
• Coefficients are also conversion factors

When doing any problem solving questions that involve stoichiometry, use the following:

What you need/What you have

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Here's some examples:

ex: Given the reaction N2 + 3H2 -----> 3NH3, how many moles of NH3 are produced when 18 mol of H2 are reacted?
- 18 mol H2 X 2 mol NH3/3 mol H2 = 12 mol

ex: How many moles of Fe are required to produce 16 mol of H2 in the reaction 3Fe + 4H2O ----->Fe3O4+ 4H2?
-# of moles of Fe = 16 mol H2 x 3 mol Fe/4 mol H2 = 12 mol

ex: According to the eqyatuon 2H2 + O2 ----> 2H2O, how many moles of H2O are produced when 9.6 mol of O2 react?
- 9.6 mol O2 x 2 mol H2O/1 mol O2 = 19 mol

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Converting to mass requires one additional step

ex: In the reaction 4NH3 + 5 O2 -----> 6H2O + 4NO, what mass of NO is produced when 2.00 mol of NH3 are reacted with excess O2?

- 2.00 mol NH3 x 4 mol NO/4mol NH3 x 30.0 g NO/ 1 mol NO = 60.0 g

ex: C5H12 (Pentane) burns according to the reaction C5H12 + 8 O2 -----> 5 CO2 + 6 H2O. What mass of O2 is required to produce 60.0 g of H2O?

- 60.0 g H2O x 1 mol H2O/18.0 g H2O x 8 mol O2/6 mol H2O x 32.0 g O2/1 mol O2 = 142 g