stoichiometry
Chemical Equations
Balancing equations
1.The Eq. must represent the
known facts.
2. The Eq. must contain the correct
formulas for reactants and products.
3. The law of conservation of mass
must be followed.
4. Balance atoms that appear once 1st.
5. Treat polyatomics as one unit if they
appear on both sides the same way.
6. Balance other elements.
7. Balance H
8. Balance O last!!
*NEVER CHANGE A SUBSCRIPT
Chemical Reactions and Equations: Basic Concepts
Topic
8
Balancing an Equation
• The balanced equation tells us that when
carbon and oxygen react, one unit of oxygen
react with each molecule of carbon to form one
unit of carbon dioxide
Conservation of Mass and Balancing
Equations
Click in this box to enter notes.
Go to Slide Show View (press F5) to play the video or animation. (To exit, press Esc.)
This media requires PowerPoint® 2000 (or newer) and the Macromedia Flash Player (7 or higher).
[To delete this message, click inside the box, click the border of the box, and then press delete.]
Copyright © Houghton Mifflin Company. All rights reserved.
Example
• Write and balance the reaction between
sodium hydroxide and calcium bromide to
give calcium hydroxide and sodium
bromide
NaOH + CaBr2  Ca(OH)2 + NaBr
• 2 NaOH + CaBr2  Ca(OH)2 + 2NaBr
Here are some more to balance:
a)
b)
c)
d)
e)
f)
g)
h)
i)
2KNO3  2KNO2 + O2
2Pb(NO3)2  2PbO + 4NO2 + O2
P4 + 6I2  4PI3
3MgO + 2H3PO4  Mg3(PO4)2 + 3H2O
Br2 + 2KI  I2 + 2KBr
Ca(OH)2 + 2HNO3  Ca(NO3)2 + 2H2O
Bi2O3 + 3H2  2Bi + 3H2O
3Fe + 2O2  Fe3O4
2CaO + 5C  2CaC2 + CO2
Classification of Reactions
• There are 5 major classifications of
reactions:
– Synthesis A + B → AB
– Decomposition AB → A + B
– Combustion Hydrocarbon + O2 → CO2 + H2O
– Single Replacement AB + C → AC + B
– Double Replacement AB + CD → AD + CB
Chemical Reactions and Equations: Basic Concepts
Topic
8
Major Classes of Reactions
• In one type of reaction, two substances—
either elements or compounds—combine to
form a compound.
• Whenever two or more substances combine
to form a single product, the reaction is called
a synthesis reaction.
Chemical Reactions and Equations: Basic Concepts
Topic
8
A Synthesis Reaction
• When iron rusts, iron
metal and oxygen gas
combine to form one
new substance,
iron(III) oxide.
• The balanced equation for this synthesis
reaction shows that there is more than one
reactant but only one product.
Chemical Reactions and Equations: Basic Concepts
Topic
8
A Synthesis Reaction
Synthesis (Combination)
• Synthesis – when 2 or more substances
react to produce 1 product
• Of the form: A + B  AB
• Examples:
– 2 Fe + 3 Cl2  2 FeCl3
– 2 Na + Cl2  2NaCl
– CaO + H2O  Ca(OH)2
– 2Mg + O2  2MgO
Synthesis # 1
1. Metal oxide + nonmetal oxide  metal
oxyanion a salt (Not Redox)
• No Redox simply means that the
oxidation numbers of the elements stays
the same
•
Oxyanion = a polyatomic ion with oxygen
Synthesis # 1 Example
• Sulfur dioxide gas is passed over solid
calcium oxide
• SO2 + CaO 
• We know that we have to get a metal
oxyanion.
• So we either get CaSO4 or CaSO3
• We need to check the oxidation states on
sulfur to see which one is the same.
Synthesis # 1 Example
•
•
•
•
•
•
•
In SO2, the oxidation number of O is -2
So the oxidation number of S must be +4
Our product choices are CaSO3 or CaSO4
In CaSO3…S has an oxidation # of +4
In CaSO4…S has an oxidation # of +6
Therefore the product must be CaSO3
SO2 + CaO  CaSO3
Chemical Reactions and Equations: Basic Concepts
Topic
8
Major Classes of Reactions
• In a decomposition reaction, a compound
breaks down into two or more simpler
substances.
• The compound may break down into
individual elements, such as when
mercury(II) oxide decomposes into mercury
and oxygen.
Chemical Reactions and Equations: Basic Concepts
Topic
8
Major Classes of Reactions
• The products may be an element and a
compound, such as when hydrogen peroxide
decomposes into water and oxygen.
• The compound may break down into simpler
compounds.
Chemical Reactions and Equations: Basic Concepts
Topic
8
A Decomposition Reaction
• When ammonium nitrate is heated to a high
temperature, it explosively breaks down into
dinitrogen monoxide and water.
• The decomposition reaction taking place is
represented by a balanced equation that shows
one reactant and more than one product.
Chemical Reactions and Equations: Basic Concepts
Topic
8
A Decomposition Reaction
Decomposition
• Decomposition – when a single compound
breaks down into 2 or more compounds
• Of the form: AB  A + B
• Note that this is the exact opposite of synthesis
• Examples:
– 2 Na3N  6 Na + N2
– NH4NO3  N2O + 2H2O
– 2H2O  2 H2 + O2
Decomposition
Synthesis
Decomposition
Redox
Metal + Nonmetal 
salt
Salt  Metal +
Nonmetal
Non Redox
Metal oxide + H2O 
base
base  Metal oxide
+ H 2O
Nonmetal oxide +
H2O  acid
acid Nonmetal
oxide + H2O
Metal oxide +
Nonmetal oxide 
salt
salt  Metal oxide +
Nonmetal oxide
More Decomposition
•
•
•
•
Metal chlorates  metal chloride + O2
(NH4)2CO3  2NH3 + H2O + CO2
2H2O2  2H2O + O2
If you get any of these products…they
decompose…
–
–
–
–
NH4OH  NH3 + H2O
H2CO3  CO2 + H2O
H2SO3  SO2 + H2O
HNO2  NO + NO2 + H2O
Chemical Reactions and Equations: Basic Concepts
Topic
8
Major Classes of Reactions
• A combustion reaction is one in which a
substance rapidly combines with oxygen
to form one or more oxides.
Click box to view movie clip.
Chemical Reactions and Equations: Basic Concepts
Topic
8
Combustion
• When welding is done
with an acetylene
torch, acetylene
combines with oxygen
to form carbon dioxide
and water.
• This combustion reaction is exothermic, and
enough energy is released to melt metal.
Chemical Reactions and Equations: Basic Concepts
Topic
8
Combustion
Combustion
• Combustion – when O2 combines with a
hydrocarbon to form CO2 and H2O
• Of the form:
hydrocarbon + O2  CO2 + H2O
• For example:
– CH4 + 2 O2  CO2 + 2H2O
– 2CH3OH + 3O2  2CO2 + 4H2O
Combustion
1.
•
•
•
Hydrocarbon + O2 CO2+ H2O (No ions)
Combustion of methane
CH4 + O2 CO2+ H2O
CH4 + 2O2 CO2+ 2H2O
When Balancing Combustion
Reactions
• Put a two in front of the hydrocarbon to
start.
• Balance them in the order C, H, O
• Make sure your answer is in the lowest
whole number ratio
Chemical Reactions and Equations: Basic Concepts
Topic
8
Major Classes of Reactions
• In a single-displacement reaction, one
element takes the place of another in a
compound.
• The element can
replace the first
part of a
compound, or it
can replace the
last part of a
compound.
Chemical Reactions and Equations: Basic Concepts
Topic
8
Single Displacement
• If an iron nail is placed into an aqueous
solution of copper(II) sulfate, the iron
displaces the copper ions in solution, and
copper metal forms on the nail.
Chemical Reactions and Equations: Basic Concepts
Topic
8
Single Displacement
Single Replacement
• Single Replacement – when the atoms of
one element replace the atoms of another
element in a compound
• Of the form : A + BX  B + AX
• For example:
– 2 Li + 2H2O  2 LiOH + H2
– Cu + 2AgNO3  2 Ag + Cu(NO3)2
Activity Series
Page 286
TABLE 3 in
your text
book
Single Replacement Reactions
• In order for a single replacement reaction to
occur, the element that is by itself must be
strong enough to push the other element out of
the way.
• The activity series show you the relative pushing
power of the elements.
• In order for the reaction to occur, the lone
element must be above the element in the
compound
• Otherwise…NO REACTION  NR
Single Replacement Reactions
• You need to know which chart you are to
look at…metals or halogens.
• A metal can replace another metal
• A halogen can replace another halogen
Will these reactions occur?
• Will the following reaction occur? If so,
complete and balance the reaction.
• Ag + Cu(NO3)2 
• Ag + Cu(NO3)2 NR
• No reaction because Ag is below Cu in the
Activity series of metals
Will these reactions occur?
• Will the following reaction occur? If so,
complete and balance the reaction.
• Mg + AlCl3 
• 3Mg + 2AlCl3 3MgCl2 + 2 Al
• The reaction WILL occur because Mg is
above Al in the activity series
Will these reactions occur?
• Will the following reaction occur? If so,
complete and balance the reaction.
• Br2 + MgCl2 
• Br2 + MgCl2  NR
• This reaction will NOT occur because Br is
not above Cl in the activity series of
halogens
Double Replacement
• Double Replacement – a reaction
involving the exchange of ions between 2
compounds
• Of the form: AX + BY  BX + AY
Chemical Reactions and Equations: Basic Concepts
Topic
8
Major Classes of Reactions
• In double-displacement
reactions, the positive
portions of two ionic
compounds are
interchanged.
• For a double-displacement
reaction to take place, at
least one of the products
must be a precipitate or
water.
Chemical Reactions and Equations: Basic Concepts
Topic
8
Double Displacement
• When clear aqueous solutions of lead(II)
nitrate and potassium iodine are mixed, a
double-displacement reaction takes place
and a yellow solid appears in the mixture.
• This solid is lead(II) iodine, and it
precipitates out because it is insoluble in
water, unlike the two reactants and the
other product.
Chemical Reactions and Equations: Basic Concepts
Topic
8
Double Displacement
Double Replacement (Metathesis)
• Double Replacement – a reaction
involving the exchange of ions between 2
compounds
• Of the form: AX + BY  BX + AY
• Examples:
– Pb(NO3)2 + 2KI  PbI2 + 2KNO3
– Na2CO3 + 2AgNO3  2NaNO3 + Ag2CO3
Double Replacement (Metathesis)
• In order for a double replacement reaction
to take place, one of 3 things must be
formed:
• Precipitate (solid)
• Gas
• Weak electrolyte – usually water
Precipitation Reactions
Click in this box to enter notes.
Go to Slide Show View (press F5) to play the video or animation. (To exit, press Esc.)
This media requires PowerPoint® 2000 (or newer) and the Macromedia Flash Player (7 or higher).
[To delete this message, click inside the box, click the border of the box, and then press delete.]
Copyright © Houghton Mifflin Company. All rights reserved.
Solubility Rules!!!
Double Replacement # 2
(Formation of a gas)
2.
•
•
•
•
•
•
Formation of a gas (acid + sulfide, sulfite, carbonate,
or bicarbonate…or ammonium salt + a strong base 
NH3(g), H2O, and a salt)
Hydrobromic acid is added to a solution of potassium
bicarbonate
HBr + KHCO3 
HBr + KHCO3  H2CO3 + KBr
H2CO3 ALWAYS breaks down into CO2 + H2O
HBr + KHCO3 CO2 + H2O + KBr
H+ + HCO3- CO2 + H2O
Double Replacement #4
(Acid Base neutralization)
• Acid + base  salt + water
• Hydrogen sulfide gas is bubbled through
excess potassium hydroxide solution
• H2S + 2KOH  2HOH + K2S
• H2S + 2K+ + 2OH-  2H2O + 2K+ + S-2
• H2S + 2OH-  2H2O + S-2
Proton Transfer
Click in this box to enter notes.
Go to Slide Show View (press F5) to play the video or animation. (To exit, press Esc.)
This media requires PowerPoint® 2000 (or newer) and the Macromedia Flash Player (7 or higher).
[To delete this message, click inside the box, click the border of the box, and then press delete.]
Copyright © Houghton Mifflin Company. All rights reserved.
Ionic Equations
Equations
• Molecular equations – show the
complete chemical formulas. Does not
indicate ionic character
• Complete ionic equation – shows all
ions. Actually how the particles exist in the
solution
Steps for Writing Ionic Equations
1. Write the balances molecular equation
(balanced chemical equation)
2. Break every thing down into its ions
EXCEPT the solid, gas, or water
(complete ionic equation)
3. Cross out everything that is the same on
both sides (spectator ions)
4. Write what is left (net ionic equation)
Rules
• When writing ionic equations, you must
keep together the solid, gas, or water
• Spectator ions – ions that appear on both
sides of the equation. They have very little
to do with the chemical reaction
Example
• Write the balanced chemical equation, the
complete ionic equation, and the net ionic
equation for the reaction between lead (II) nitrate
and potassium iodide. Solid potassium iodide
will be formed.
Example
•
•
•
•
•
Write the balanced chemical equation
Pb(NO3)2 + 2 KI  PbI2 + 2 KNO3
You MUST identify the solid, gas, or water
Pb(NO3)2 + 2 KI  PbI2 (s) + 2 KNO3
Balanced chemical equation
Example
• Now break every thing except the solid,
gas, or water into its ions
• Remember ions are things with charges
• Everything will be broken down into one
positive charge and one negative charge
Example
• Pb(NO3)2 + 2 KI  PbI2 (s) + 2 KNO3
• Pb+2 + 2NO3-1 + 2K+1 + 2 I -1  PbI2 (s) + 2K+1 + 2NO3-1
• Complete ionic Equation
Example
• Now cross out everything that is the same on
both sides (spectator ions)
• Pb+2 + 2NO3-1 + 2K+1 + 2 I -1  PbI2 (s) + 2K+1 + 2NO3-1
• Pb+2 + 2NO3-1 + 2K+1 + 2 I -1  PbI2 (s) + 2K+1 + 2NO3-1
• Now write what is left
• Pb+2 + 2 I -1  PbI2 (s)
• Net ionic equation
Another Example
• Write the balanced chemical equation,
complete ionic equation, and net ionic
equation for the reaction between calcium
chloride and sodium carbonate. Solid
calcium carbonate will be formed.
Another Example
• Balanced chemical equation
• CaCl2 + Na2CO3  CaCO3 (s) + 2NaCl
• Complete ionic equation
• Ca+2 + 2Cl -2 + 2Na +1 + CO3 -2  CaCO3 (s) + 2Na +1 + 2Cl -1
• Net Ionic Equation
• Ca+2 + 2Cl -2 + 2Na +1 + CO3 -2  CaCO3 (s) + 2Na +1 + 2Cl -1
• Ca+2 + CO3 -2  CaCO3 (s)
What if water is formed?
• Write the balanced chemical equation,
complete ionic equation, and net ionic
equation for the reaction between Calcium
hydroxide and nitric acid
Example with water
• Balanced chemical equation
• Ca(OH)2 + 2 HNO3  Ca(NO3)2 + 2 HOH
• Complete ionic equation
• Ca+2 + 2(OH) -1 + 2H+1 + 2NO3 -1  Ca+2 + 2NO3 -1 + 2 HOH
• Net Ionic Equation
• Ca+2 + 2(OH) -1 + 2H+1 + 2NO3 -1  Ca+2 + 2NO3 -1 + 2 HOH
• 2(OH) -1 + 2H+1  2 HOH
Stoichiometry
• Using the methods of stoichiometry, we
can measure the amounts of substances
involved in chemical reactions and relate
them to one another.
Stoichiometry Rules
• 1. Balance the equation.
• 2. convert all units to moles
• 3. use a molar ratio from the balanced
equation to compare what is given to what
you want.
• 4. convert back from moles to the unit the
question asks for.
• Always no matter what unit you are given
convert it to moles before you make a
comparison.
Coefficients
• Coefficients in a balanced chemical RXN
can represent any of the following
• 1. moles
• 2. molecules of a compound
• 3. volume of a gas at STP. (22.7 L=1mol)
• * they never represent mass.
Mole – Mole Relationship
• 4 Fe + 3O2  2Fe2O3
• 4 mol Fe / 3 mol O2
• 4 mol Fe / 2 mol Fe2O3
• 3mol O2 / 2 mol Fe2O3
Mole – Mole Relationship
• How many moles of Fe2O3 will I form from
5.0 mol of Fe?
• 5.0 mole Fe x 2 mol Fe2O3
4 mol Fe
• 2.5 mol Fe2O3
Conversion Factor # 3
# Moles A
# Moles B
The #’s in from if A & B MUST come from
the balanced chemical equation
Mass – Mole Relationship
• How many g of NaCl will be produced from
1.25 mol of chlorine gas reacting with
sodium?
• Write the reaction
• Na + Cl2  NaCl
• Balance the reaction
• 2Na + Cl2  2NaCl
Mass – Mole Relationship
• Work the problem
• 1.25 mol Cl2 x 2 mol NaCl x 58.44 g NaCl
•
1 mol Cl2
1 mol NaCl
• 146 g NaCl
Mass – Mass Relationships
• Ammonium nitrate decomposes into
dinitrogen monoxide gas and water.
Determine that amount of water produced
if 25.0 g of ammonium nitrate
decomposes.
• NH4NO3  N2O + H2O
• NH4NO3  N2O + 2 H2O
Mass – Mass Relationships
• 25.0 g NH4NO3 x 1 mol NH4NO3 x 2 mol H2O
x 18.02 g H2O
80.04 g NH4NO3 1 mol NH4NO3
1 mol H2O
• 11.2 g H2O