Stoichiometric

Example: From the following reaction determine how many FeCl${}_3$ molecules can be produced from 150 atoms of Fe reacting with unlimited Cl${}_2$?

Fe (s) + Cl${}_2$ (g) -> FeCl${}_3$ (s)

Balanced: 2 Fe (s) + 3 Cl${}_2$ (g) -> 2 FeCl${}_3$ (s)

Cl${}_2$ is a molecule not an atom

What if you had 2.75 mol of iron Then how much FeCl${}_3$ (s) would you end up with? 2.75 mol of FeCl${}_3$ because of the 1:1 ratio

Steps

1. Balance
2. Convert atoms of given to moles of given (if necessary)
3. Convert moles of given to moles of unknown using the Mole Ratio between given and unknown
4. Convert moles unknown to molecules or mass

Mass of oxygen required to consume 6.80g of ammonia NH${}_3$ + O${}_2$ -> NO + H${}_2$O

Balance: 4 NH${}_3$ + 5 O${}_2$ -> 4 NO + 6 H${}_2$O

n = m / M = 6.80g / 17.04 g / mol = 0.399061 mol NH${}_3$ Use Molar Mass formula

n = 0.399061 mol NH${}_3$ * 5 mol O${}_2$ / 4 mol NH${}_3$ = 0.4988263

Now we have # of moles of oxygen we are looking for but we are looking for mass of oxygen required

m = N * M = 0.4988263 mol * 32.00 g / mol

= 15.962441g = 16.0g O${}_2$ (Round using Significant Digits)

To convert from number of moles to the number of molecules multiply the number of moles to Avogardo’s Constant

Homework (Grade 11 Chemistry)

p.298 # 1 - 10 p.300 # 11 - 20 p.304 # 21 - 30 p.305 # 1 - 12