Transcript Stoichiometric Calculations

Stoichiometric Calculations
Doesn’t that sound fun!!!
Using Stoichiometry

Mole to mole conversions-Start with a
balanced chemical reaction!
◦ 2K + 2H20 -> 2KOH + H2
How can you determine the number of
moles of hydrogen produced when
0.0400 mol of potassium is used?
 Simply take your given and multiply by
your needed mole ratio!
 0.0400 mol K x __________=

General equation
Mol of known x mol of unknown

mole of known


= moles of unknown!

You must find the correct mole
ratio and place it in the equation
mol of known -> mol of unknown
Let’s practice!
How many moles of CO2 are produced
when 10 moles of propane (C3H8) are
burned in a gas grill?
 C3H8 + 5O2 -> 3CO2 + 4H2O

Do these in your notebook!
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2 SO2 + O2 + 2H20 ->2H2SO4
◦ If 12.5 mol SO2 reacts, how many mol of
H2SO4 can be produced?
◦ How many mol O2 is needed?

2CH4 + S8 -> 2CS2 + 4H2S
◦ Calculate the mole CS2 produced when 1.5
mol of S8 is used.
◦ How many mol of H2S would be produced?
Mole to mass conversion
For these you simply take the next step!
 General equation:

Mol known x mol unknown x mass unknown

mol known
mol unknown
 It’s just adding what we’ve done last unit to the
new mole ratio!

mol of known -> mol of unknown -> g of unknown
Let‘s try one!

2Na + Cl2 -> 2NaCl
◦ Determine the mass of NaCl produced when
1.25 mol of Cl2 reacts with Na.
Now you try in your notebook!

TiO2 + C + 2Cl2 -> TiCl4 + CO2
◦ If you begin with 1.25 mol TiO2, what mass of
Cl2 gas is needed?

2NaCl -> 2Na + Cl2
◦ How many grams of Cl2 can be obtained
from 2.50 mol NaCl?
Let’s get really crazy!
If you were getting ready to carry out a
chemical reaction in the lab, you would
need to know how much of each reactant
to use in order to get the mass of product
you needed.
 This is where mass to mass conversions
come in!
 If given mass, convert to moles. Then use
your mole ratio to go to moles of the other
substance. Finally convert back to mass!

Steps in stoichiometric calculations
Make sure you have a balanced equation.
Interpret the equation in terms of moles.
2. Determine the moles of the given substance
using a mass to mole conversion. (molar mass!)
3. Determine the moles of the unknown substance
from the moles of the given substance (mole
ratio!)
4. From the moles of the unknown substance,
determine the mass of the unknown using a mole
to mass conversion (molar mass!)
1.
g of known->mol of known->mol of unknown->g of unknown
Let’s try one!

NH4NO3 ->N2O + 2H2O
◦ Determine the mass of water produced from
the decomposition of 25.0 g of NH4NO3.
You try!

2NaN3 -> 2Na + 3N2
◦ Determine the mass of N2 produced if 100.0g
NaN3 is decomposed.
Assessment
1.
2.
3.
4.
Why is a balance equation needed in
solving stoichiometric calculation?
When solving stoichiometric problems,
how is the correct mole ratio expressed?
List the 4 steps in solving stoich problems.
Describe how a chemical engineer would
determine the mass of bromine needed to
react completely with a given mass of
magnesium.