#### Transcript Stoichiometry

```Balancing Hints:
 Balance the metals first.
 Balance the ion groups next.
 Balance the other atoms.
 Save the non ion group oxygen and
hydrogen until the end.
 Balance the following equations;
__Ca + __H2O → __H2 + __ Ca(OH)2
__ Cu + __ O2 → __ CuO
__ Na + __ O2 → __ Na2O
__ Fe + __ HCl → __ FeCl2 + __ H2
__ Fe + __ Br2 → __ FeBr3
__ C4H8 + __ O2 → __ CO2 + __ H2O
 Balance this equation showing the
burning of methane below, to answer the
following questions.
 __ CH4 + __ O2 → __ CO2 + __ H2O
How many grams of oxygen are required
to produce 2.23 g of carbon dioxide?
How many grams of water will be
produced when 34.0 g of methane is
burned?
Steps for Combustion Analysis Problems
1. Calculate the moles of CO2 produced (same as mols of C)
2. Calculate the moles of H2O produced Multiply this
number by two to calculate the number of moles of H atoms
present in the original compound.
3. Calculate the mass of C and H
4. If there is another element present (typically O) in the
combusted substance then calculate its mass by subtracting
the mass of C and H from the total mass of the combusted
sample.
5. Once you have determined the mass of each piece of the
original compound the problem can be solved just like an
empirical formula problem.
Combustion Analysis
 A sample of a common alcohol with a mass of 4.599 g,
containing C, H and O, was combusted in excess
oxygen to yield 8.802 g of CO2 and 5.394 g of H2O.
 The alcohol contains only carbon, hydrogen, and
oxygen. What is the empirical formula of the acid?
Limiting Reagent
The limiting reagent is the reactant in a chemical
reaction which limits the amount of products that
can be formed.
The limiting reagent in a chemical reaction is present
in insufficient quantity to consume the other
reactant(s).
This situation arises when reactants are mixed in
non-stoichiometric ratios.
Let’s Try This Problem Together
 H2(g) + O2(g) → H2O(l)
Calculate the stoichiometric ratio of moles H2 to moles O2
b. The moles of water created when 1.50 mol H2 is mixed
with 1.00 mol O2
c. the limiting reactant (H2 or O2) for the mixture in (b)
Let’s Try This Problem Together
 For the reaction: Na2O + H2O → NaOH
What weight of NaOH could be made from 12.4 g of
Na2O and 42.1 g of H2O?
What would be the limiting reagent if 100 g each of
Na2O and H2O were allowed to react?
Percent Yield
 Theoretical yield - The maximum amount of a given
product that can be formed when the limiting reactant
is completely consumed.
 Actual yield - amount produced in a reaction. Should
be less than the theoretical yield and provided some
where in the problem.
 Percent yield – (the actual / theoretical yield) x 100%
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