Stoichiometry
Stoichiometry
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Stoichiometry is the study of the mass
relationships of the reactants and the
products in a chemical reaction.
How much stuff it takes to make a certain
amount of new stuff.
Based on the law of conservation of mass
Mass of the reactants must equal the mass
the products
CH3OH(g) + O2(g)  CO2(g) + H2O(g)
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Chemical reactions are mole ratios between
the reactants and the products – not a mass
ratio!
Mole ratio – the ratio of moles of any two
substances in a chemical reaction
2CH3OH(l) + 3O2(g)  2CO2(g) + 4H2O(g)
2 mol CH3OH : 2 mol CO2
3 mol O2 : 4 mol H2O
There is not a direct relationship between
masses of individual reactants and products.
Must use the mole ratio to convert!
R1
+
R2
→
P1
+
P2
grams
molar mass
R1
moles R1
grams
molar mass
P2
moles P2
moles R1
(mole ratio)
moles P2
Guidelines for Stoichiometry
1.
2.
3.
4.
Write a balanced equation for the chemical
reaction.
Convert grams A to moles of A using the
molar mass.
Convert moles of A to moles of B using the
mole ratio.
Convert moles of B to grams of B using the
molar mass.
3. Examples
24. Sulfuric acid reacts with sodium hydroxide to
form sodium sulfate and water. How many
grams of Na2SO4 are produced from 25.0 g of
H2SO4?
25. In the reaction from #24, I need 550.0 g Na2SO4.
What mass of each reactant is required?
26. How much oxygen will be required to react with
100.0 g KCl to produce KClO3.
27. What mass of hydrogen peroxide must
decompose to produce 0.77 g of water? The
other product is oxygen gas.
28. Space vehicles use solid lithium hydroxide to
remove exhaled carbon dioxide according to the
equation: LiOH + CO2  Li2CO3 + H2O.
Determine the mass of carbon dioxide removed if
the space vehicle carries 1.00 kg of LiOH.
29. How many grams of carbon dioxide are
produced when 2.50 g of baking soda react with
excess citric acid (H3C6H5O7) to produce
Na3C6H5O7, carbon dioxide, and water.
30. Aspirin (C9H8O4) is produced when salicylic acid
(C7H6O3) reacts with acetic anhydride (C4H6O3)
according to the equation C7H6O3 + C4H6O3 
C9H8O4 + HC2H3O2. Determine the mass of
aspirin produced when 150.0 g of salicylic acid
reacts with an excess of acetic anhydride.