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Reaction Stoichiometry
Chapter 9 Notes
Reaction Stoichiometry Problems
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Problem Type 1: Given and Unknown
quantities are given in moles.
Amount of given substance (in moles) →
Amount of unknown substance (in moles)
Reaction Stoichiometry Problems
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Problem Type 2: Given is an amount in moles
and the Unknown is a mass in grams.
Amount of given substance (in moles) →
Amount of unknown substance (in moles) →
Mass of unknown substance (in grams)
Reaction Stoichiometry Problems
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Problem Type 3: Given is a mass in grams
and the Unknown is an amount in moles.
Mass of given substance (in grams) → amount
of given substance (in moles) → amount of
unknown substance (in moles)
Reaction Stoichiometry Problems
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Problem Type 4: Given is a mass in grams
and the Unknown is a mass in grams.
Mass of given substance (in grams) → amount
of given substance (in moles) → amount of
unknown substance (in moles) → mass of
unknown substance (in grams)
Reaction Stoichiometry Problems
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Mole Ratio: conversion factor that relates the
amounts in moles of any two substances
involved in a chemical reaction.
2Al2O3 → 4Al + 3O2
2HgO → 2Hg + O2
4NH3 +6NO → 5N2 +6H2O
Ideal Stoichiometry Calculations
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Conversions of Quantities in Moles
In a spacecraft, the carbon dioxide exhaled by
astronauts can be removed by its reaction with
lithium hydroxide according to the following
equation:
CO2(g) + 2 Li(OH)(s) → Li2CO3(s) + H2O(l)
How many moles of lithium hydroxide are
required to react with 20 mol of CO2, the
average amount exhaled by a person each day?
Conversions of Quantities in Moles
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Ammonia, NH3, is widely used as a fertilizer
and in many household cleaners. How many
moles of ammonia are produced when 6 moles
of hydrogen gas react with an excess of
nitrogen gas?
Conversions of Quantities in Moles
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The decomposition of potassium chlorate,
K(ClO3), is used as a source of oxygen in the
laboratory. How many moles of potassium
chlorate are needed to produce 15 moles of
oxygen?
Conversions of Amounts in Moles to
Mass
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In photosynthesis, plants use energy from the
sun to produce glucose, C6H12O6, and oxygen
from the reaction of carbon dioxide and water.
What mass of glucose is produced when 3.00
moles of water react with carbon dioxide?
Ideal Stoichiometry Calculations
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What mass of carbon dioxide is needed to
react with 3.00 moles of H2O in a
photosynthetic reaction?
When magnesium burns in air, it combines
with oxygen to form magnesium oxide. What
mass of magnesium oxide is produced from
2.00 moles of magnesium?
Conversion of Mass to Amounts in
Moles
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The first step in the industrial manufacture of
nitric acid is the catalytic oxidation of
ammonia.
NH3 + O2 → NO + H2O (not balanced)
The reaction is run using 824g of NH3 and
excess oxygen.
How many moles of NO are formed?
How many moles of H2O are formed?
Conversion of Mass to Amounts in
Moles
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Oxygen was discovered by Joseph Priestley in
1774 when he heated mercury (II) oxide to
decompose it to form its constituent elements.
How many moles of mercury (II) oxide are
needed to produce 125g of oxygen?
How many moles of mercury are produced?
Mass to Mass Calculations
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Tin (II) fluoride is used in some toothpastes.
It is made by the reaction of tin with hydrogen
fluoride. How many grams of SnF2 are
produced from the reaction of 30.00g of HF
with Sn?
Mass to Mass Calculations
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Laughing gas (N2O) is sometimes used as an
anesthetic in dentistry. It is produced when
ammonium nitrate is decomposed to form
N2O and water.
How many grams of NH4NO3 are required to
produce 33.0g of N2O?
How many grams of water are produced in this
reaction?
Mass to Mass Calculations
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When copper metal is added to silver nitrate in
solution, silver metal and copper (II) nitrate
are produced. What mass of silver is produced
from 100.0g of Cu?
What mass of aluminum is produced by the
decomposition of 5.0 kg of Al2O3?
Gas Stoichiometry
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You can apply the discoveries of Gay-Lussac
and Avogadro to calculate the stoichiometry of
reactions involving gases
For gaseous reactants or products, the
coefficients in chemical equations not only
indicate mole ratios but also reveal volume
ratios.
2 CO(g) + O2(g) → 2 CO2(g)
Gas Stoichiometry
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Propane, C3H8, is a gas that is sometimes used
as a fuel for cooking and heating. The complete
combustion of propane occurs according to the
following balanced equation.
C3H8(g) + 5 O2(g) → 3 CO2(g) + 4H2O(g)
What will be the volume, in liters, of oxygen
required for the complete combustion of 0.350L
of propane?
Gas Stoichiometry
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C3H8(g) + 5 O2(g) → 3 CO2(g) + 4H2O(g)
What will be the volume of carbon dioxide
produced in the reaction?
What volume of hydrogen gas is needed to
completely react with 4.55 L of oxygen gas to
produce water vapor?
Gas Stoichiometry
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What volume of oxygen gas is needed to react
completely with 0.626 L of carbon monoxide to
form gaseous carbon dioxide?
Nitric acid can be produced by the reaction of
gaseous nitrogen dioxide with water:
3 NO2(g) + H2O(g) → 2 HNO3(l) + NO(g)
If 708 L of NO2 gas react with water, what
volume of NO gas will be produced?
Gas Stoichiometry
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One mole of any gas takes up the same volume
at the same temperature as one mole of any
other gas.
In order to make stoichiometric comparisons,
chemists use Standard Temperature and
Pressure when measuring Standard Molar
Volume.
At STP 1 mole of any gas occupies 22.4 Liters.
Gas Stoichiometry
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What volume does 0.0685 mol of gas occupy at
STP?
What quantity of gas, in moles, is contained in
2.21 L at STP?
At STP, what is the volume of 7.08 mol of
nitrogen gas?
A sample of hydrogen gas occupies 14.1 L at
STP. How many moles of the gas are present?
Limiting Reactants
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The limiting reactant is the reactant that is
used up first. When the limiting reactant is
gone, the reaction stops.
The excess reactant is the reactant left after the
limiting reactant is gone.
It is analogous to making a cheese sandwich.
Limiting Reactants
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Silicon dioxide is usually quite unreactive but
reacts readily with hydrogen fluoride.
SiO2(s) + 4HF(g) → SiF4(g) + 2H2O(l)
If 6 mol HF is added to 4.5 mol SiO2, which is
the limiting reactant?
Limiting Reactants
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Some rocket engines use a mixture of hydrazine,
N2H4, and hydrogen peroxide, H2O2, as the
propellant. The equation is:
N2H4(l) + 2H2O2(l) → N2(g) + 4H2O(g)
Which is the limiting reactant in this reaction
when 0.750 mol hydrazine is mixed with 0.500
mol hydrogen peroxide?
Limiting Reactants
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N2H4(l) + 2H2O2(l) → N2(g) + 4H2O(g)
How much of the excess reactant, in moles,
remains unchanged?
How much of each product, in moles, is
formed?
Limiting Reactants
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The black oxide of iron, Fe3O4, occurs in
nature as the mineral magnetite. This substance
can also be made in the laboratory by the
reaction between red – hot iron and steam
according to the following equation.
3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)
When 36.0 g H2O is mixed with 67.0 g Fe,
which is the limiting reactant?
Limiting Reactants
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3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)
What mass in grams of black iron oxide is
produced?
What mass in grams of excess reactant remains
when the reaction is complete?
Limiting Reactants
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Zinc and sulfur, S8(s) react to form zinc sulfide.
8Zn(s) + S8(s) → 8ZnS(s)
If 2.00 mol of Zn are heated with 1.00 mol of S8
identify the limiting reactant.
How many moles of excess reactant remain?
How many moles of the product are formed?
Limiting Reactants
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Carbon reacts with steam to produce hydrogen
and carbon monoxide.
If 2.40 mol of carbon are exposed to 3.10 mol
of steam, identify the limiting reactant.
How many moles of each product are formed?
What mass of each product is formed?
Percentage Yield
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The theoretical yield is the maximum amount
of product that can be produced from a given
amount of reactant.
The actual yield is the measured amount of a
product obtained from a reaction.
P. Y. = actual yield/theoretical yield x 100
Percentage Yield
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Chlorobenzene, C6H5Cl, is used in the
production of many important chemicals, such
as aspirin, dyes, and disinfectants. One
industrial method of preparing chlorobenzene is
to react benzene, C6H6, with chlorine.
C6H6(l) + Cl2(g) → C6H5Cl(l) + HCl(g)
When 36.8 g benzene react with an excess of
Cl2, the actual yield of chlorobenzene is 38.8 g.
What is the percentage yield of chlorobenzene?
Percentage Yield
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Methanol can be produced through the reaction
of CO and H2 in the presence of a catalyst.
CO(g) + 2H2(g) → CH3OH(l)
If 75.0 g of CO reacts to produce 68.4g
CH3OH, what is the percentage yield of
CH3OH?
Percentage Yield
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Aluminum reacts with excess copper(II) sulfate
according to the reaction below. If 1.85 g of
aluminum react and the percentage yield of Cu is
56.6%, what mass of Cu is produced?
Al(s) + CuSO4(aq) → Al2(SO4)3(aq) + Cu(s)
(unbalanced)