Download Stoichiometry mass relations

Stoichiometry
Mass Calculations
Chemistry 11
Ms. McGrath
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.
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 28.02 g/mol N2 = 28.02 g N2
3 mol H2 x 2.02 g/mol H2 = 6.06 g H2
2 mol NH3 x 17.04 g/mol NH3 = 34.08 g NH3
Mass relationships in chemical equations
Balanced
equation
Number of
particles
Amount (mol)
Mass (g)
Total mass (g)
N2(g) + 3H2(g)  2NH3(g)
1 molecule N2 reacts with 3 molecules H2
to produce 2 molecules NH3
1 mol N2 + 3 mol H2  2 mol NH3
28.02 g N2 + 6.06 g H2  34.08 g NH3
34.1 g reactants  34.1 g products
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.
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.
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 if each astronaut produces
1.00 x 103 g of carbon dioxide each day?
Stoichiometry - Example
Strategy:
1. Write a balanced equation
2. Convert the given mass of CO2 to the
number of moles of CO2
3. Calculate the number of moles of LiOH
based on the mole ratios
4. Convert the number of moles to mass of
LiOH
Stoichiometry
Try page 121, #11 - 13