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CHAPTER 9
Chemical Quantities
CHAPTER 9 TERMS
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Stoichiometry – the process of using a chemical
equation to calculate the relative masses of reactants
and products involved in a reaction.
Mole ratios – conversion factors based on the
balanced chemical equation (i.e., coefficients).
Limiting reagent (reactant) – the reactant the is
consumed first and limits the amounts of products
that can be formed.
Percent Yield – the actual yield of product compared
to the theoretical yield, expressed as a percent.
Theoretical Yield – the amount of substance that
can be produced (mathematically speaking).
Actual Yield – the amount of substance actually
produced.
STEPS FOR CALCULATING THE MASSES OF
REACTANTS AND PRODUCTS IN CHEMICAL
REACTIONS
1.
2.
3.
4.
5.
6.
7.
Write the chemical equation. Do not forget to use
phase labels.
Balance the equation for the reaction.
Write down the given information directly below the
corresponding formula.
Place a ? under the formula which the mass is
unknown.
Convert the masses of reactants or products to moles.
Use the balanced equation to set up the appropriate
mole ratio(s).
Use the mole ratio(s) to calculate the number of moles
of the desired reactant or product.
STEPS FOR SOLVING STOICHIOMETRY
PROBLEMS INVOLVING LIMITING
REAGENTS.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Write the chemical equation. Do not forget to use phase
labels.
Balance the equation for the reaction.
Write down the given information directly below the
corresponding formula.
Place a ? under the formula which the mass is unknown.
Convert the masses of reactants to moles.
Divide each the moles of the reactants by their respective
coefficients.
The smallest number is the limiting reactant. Use this
number of find the required information.
Use the balanced equation to set up the appropriate mole
ratio(s).
Use the mole ratio(s) to calculate the number of moles of the
desired reactant or product.
Convert from moles back to masses (grams, etc.)
EXAMPLES
1.
2.
3.
Calculate the mass of carbon dioxide produced
when 96.1 g of propane (C3H8) reacts with
sufficient oxygen.
Calculate the mass of water formed by the
complete reaction of 96.1 g of propane with
oxygen.
Hydrofluoric acid reacts with silicon dioxide to
produce silicon tetrafluoride and water.
a.
b.
How many grams of HF are needed to react with
5.68 g of silicon dioxide?
Calculate the mass of water produced.
EXAMPLES
4.
5.
6.
Carbon monoxide reacts with hydrogen to produce
methanol (CH3OH). How many grams of carbon
dioxide and what mass of hydrogen are needed to form
6.0 kg of methanol?
Lithium nitride is prepared by the reaction of lithium
metal and nitrogen gas. Calculate the mass of lithium
nitride formed from 56.0 g of nitrogen gas and 56.0 g of
lithium.
Titanium (IV) oxide can be prepared by reacting
gaseous titanium (IV) chloride with oxygen gas. A
second product of this reaction is chlorine gas.
a.
b.
Suppose 6.71 x 103 g of titanium (IV) chloride is reacted with
2.45 x 103 g of oxygen. Calculate the maximum mass of
titanium (IV) oxide that can form.
If the percent yield of TiO2 is 75%, what mass is actually
formed?