1. Stoichiometry
Chemistry 11
Ms. McGrath

2. Mass relationships in chemical equations
As we saw, the coefficients in a chemical equation represents number of particles as well as moles. We can, therefore, use the molar masses to determine the mass ratios for a reactions.

3. Mass relationships in chemical equations
N2(g) + 3H2(g) -> 2NH3(g) For the above reaction, we can calculate the mass of each substance. 1 mol N2 x g/mol N2 = g N2 3 mol H2 x 2.02 g/mol H2 = 6.06 g H2 2 mol NH3 x g/mol NH3 = g NH3

4. Mass relationships in chemical equations
Balanced equation
N2(g) + 3H2(g) -> 2NH3(g)
Number of particles
1 molecule N2 + 3 molecules H2 ->
2 molecules NH3
Amount (mol)
1 mol N2 + 3 mol H2 -> 2 mol NH3
Mass (g)
28.02 g N g H2 -> g NH3
Total mass (g)
34.1 g reactants -> 34.1 g products

5. Mass relationships in chemical equations
The Law of Conservation of Mass During a chemical reaction, the total mass of the reactants is always equal to the total mass of the products. If we determine the total mass of substances on each side of a balanced chemical reaction, we will find that the mass of the products is always equal to the mass of the reactants.

6. Stoichiometry
Stoichiometry is the study of the relative quantities of reactant and products in a chemical reaction. Gravimetric stoichiometry is the analysis involving mass of the reactants and products.

7. Stoichiometry Stoichiometric calculations are carried out for
many reasons. Some involve a matters of life
and death.
For example: in a spacecraft, a closed
system, carbon dioxide is produced by
astronauts. This air must be passed through
lithium hydroxide canisters.
How do engineers determine how much
lithium oxide is required?

8. Stoichiometry - Example
In a spacecraft, a closed system, carbon
dioxide that is produced by astronauts
can be removed with lithium hydroxide.
The reaction produces lithium carbonate
and water. What mass of lithium
hydroxide should engineers put on
board a spacecraft, per astronaut, for
each day?

9. Stoichiometry - Example
Strategy:
Write a balanced equation.
Convert the given mass of CO2 to
the number of moles of CO2.
Calculate the number of moles of
Li2CO3 based on the mole ratios.
4. Convert the number of moles to
mass.