Stoichiometry 101 
By T. Webb HHS
This term refers to the process of predicting how much of one substance will react with
another, or how much will be produced in a given reaction. It is based on the number of
moles of the respective substances found in an equation, and involves the “mol ratio” to
convert the relative amount of the unknown substance to the known amount. It is very
similar to the process you would use to calculate the relative amounts of ingredients in a
recipe if you decided to double or triple the batch.
If a recipe called for 1 c flour, ½ tsp salt and 1 tsp vanilla, you would need how much of
each if you tripled it? ___ c flour, ____ tsp salt, ___ tsp vanilla
To do stoichiometry, you need a balanced equation, so that you know how many moles
of each substance is involved.
2 NH3 (g)


1 N2 (g) + 3 H2 (g)
How many moles of product would result if this was doubled?
If I started with 0.592 mol of ammonia?
The mol ratio determines the equivalent values quickly, by simply multiplying the known
substance by the ratio of the unknown over the known.
For example, given 2 H2 (g) + 1 O2 (g)
2 H2O (l), knowing that you have 4.13 mol O2,
how many moles of H2 would that be?
The mol ratio would be 2 mol (H2 ?) X 4.13 mol O2 ; therefore needing 8.26 mol H2
1 mol (O2 !)
NOTE: If you are given mass or volume units, you must convert them to moles
before using the mol ratio. Likewise, if your answer is required to be in mass
or volume units, you would convert after the mol ratio step. Moles in, mole
ratio, moles out…
Example 2:
Given 2 NH4Cl (aq) + 1 Ca(OH)2 (s)
2 NH4OH (aq) + 1 CaCl2 (aq)
1. How many moles of the NH4OH would result from 23 mol of Ca(OH)2?
2. How many moles of Ca(OH)2 would be required to react with 135.2 g of NH4Cl?
3. What mass of CaCl2 would be produced from the mass in #2?
If you are given:
Unit answer is in:
Mass – use n=m/M = mol
Mass – use mol x M= m
MOL RATIO
Moles – go directly to ratio
Moles – from ratio
Volume – use n=v/V = mol
Volume – use mol x V= v
1. How many moles of oxygen will be needed to react with 0.26 mol of P4?
___ O2 (g) + ___ P4 (g) ___ P4O10 (s)
2. In the combustion of octane gas, C8H18 (g), how many moles of oxygen will react
with 6.14 mol of octane?
3. ___ Na (s) + ___ HOH (l)
___NaOH (aq) + ___ H2 (g)
Mass?
4. ___Ca(OH)2 (s) + ___CO2 (g)
Mol?
5. ___C6H12O6 (s) + ___O2 (g)
Mass?
0.540 mol
___ CaCO3 (s) + HOH (l)
96.3 g
___CO2 (g) + ___H2O (l)
78.33 g
6. Carbon reacts with hydrogen to produce octane gas. What volume of H 2 (g) will
produce 12 mol of octane?
7. What volume of butane (C4H10) will burn to produce 0.23 L of CO2 (g)?
8. ___Fe (s) + ___H2SO4 (aq)
___ H2 (g) + ___ Fe2(SO4)3 (aq) Given 142.4 g of
Fe, what mass of iron (iii) sulfate will be produced?
9. If you had 100.0 g of sucrose, how many moles would that be?
10. You have 0.400 mol of HCl (aq) reacting with magnesium hydroxide. What mass
of magnesium chloride will result?
11. What volume of oxygen is required for the mass given in question 5 above?
12. In a simple composition reaction of H2 and O2 producing water, given 250 kg of
H2 (g), what mass of water would result? What volume of O2 is required?