Transcript Unit 7: Chemical Equations & Reactions


Ionic compounds can form from transition
metals
◦ Transition metals do not always follow the patterns that we
discussed
 Can have more than one oxidation number (charge)

To identify the charges of transition metals,
roman numerals are placed in their name,
directly after the transition metal
◦ The number of the roman numeral is equal to the charge
I = +1
II = +2
III = +3
IV = +4

Examples:
Iron (II) chloride
Iron (III) oxide
Fe+2 Cl-1
FeCl2
Fe+3 O-2
Fe2O3
You will need to be able to write the formulas
of these compounds from their name


On page 11, shade in the following metals in
ORANGE and update your key
Then write in their possible charges in each box
◦
◦
◦
◦
◦
◦
◦
◦
◦
◦
◦
◦
◦
24
25
26
27
28
29
30
47
48
50
79
80
82
Chromium: +2, +3
Manganese: +2, +3, +4
Iron: +2, +3
Cobalt: +2, +3
Nickel: +2, +3
Copper: +1, +2
Zinc: +2
Silver: +1
Cadmium: +2
Tin: +2, +4
Gold: +1, +3
Mercury: +1, +2
Lead: +2, +4
Write the formulas of the following compounds:
1. nickel (II) chloride
Ni+2 Cl-1
2. copper (II) nitrate
Cu+2 NO3-1 Cu(NO3)2
3. iron (III) hydroxide
Fe+3 OH-1
Fe(OH) 3
4. Gold (I) oxide
Au+1 O-2
AuO2
NiCl2

A change in the size, shape, state of matter, etc.
that does not change the identity of a substance
◦ A phase change is a physical change even though energy
may be removed or added to the substance
 In the new state of mater, the substance is still made of
the same components, the atoms just have more or
less energy (phase changes are the only physical
changes that have energy changes)
 i.e. if liquid water evaporates, it becomes water vapor
if water vapor condenses, it becomes liquid water

The change of one substance into a
new substance (chemical reaction)
◦ A chemical change alters the original
chemical make-up of the substance
◦ Energy changes and physical changes
always accompany chemical changes
How can you tell if a chemical change has
taken place?
◦ ENERGY
Evolution of heat, light, and/or sound
(sometimes heat can be absorbed too)
◦ GAS
A gas is produced, bubbles (effervescence)
◦ PRECIPITATE
When solid particles form from 2 liquids
◦ COLOR – Unexpected Color change
(i.e. clear liquid + clear liquid  purple liquid)

When energy flows out of the system as heat,
the process is exothermic.
• Usually feels warm
 Ex: Combustion of a match, hand warmers

Processes that absorb energy from the
surroundings are endothermic.
◦ Usually feels cool
◦ Ex: Melting ice cubes, ice packs

Reactants – the substances that exist before a

Products – the new substance(s) that are formed

chemical change (or reaction) takes place.
during the chemical changes.
CHEMICAL EQUATION – a description of a chemical
reaction that uses chemical formulas and symbols
to indicate the reactants and products of a
reaction.
REACTANTS  PRODUCTS
“Produces,” “Forms,” or “Yields”; indicates result of reaction
+
(s)
(l)
“plus”
A reactant or product in the solid state;
also used to indicate a precipitate
A reactant or product in the liquid state
(g)
A reactant or product in the gaseous state
(aq)
A reactant or product dissolved in water (in an aqueous
solution)

7 elements
◦ Molecules made out of 2 atoms (“di” = 2, “atomic” = atoms)
 Some elements are never found alone and will always bond with
another atom of the same type to become stable (O2, N2, H2, etc.)
◦ Hydrogen and the other 6 elements form a “7” shape
(nitrogen has an atomic number of 7)
On page 11,
shade these
7 elements
in YELLOW
and add to
your key
Write the equation for the reaction of methane gas
(carbon tetrahydride) with oxygen to form carbon dioxide
and water.
CH4 (g) +
O2 (g)
Reactants
CO2 (g) +
H2O (l)
Products
Notes:
• Water will always be a liquid, unless stated otherwise in the problem
• Oxygen is a diatomic molecule and will always be a gas
• Carbon dioxide will always be a gas, unless stated otherwise in the problem
• If the state of matter is not indicated in the word problem, always assume
the element/compound is in it’s normal state at room temperature
Write an equation for the reaction between chlorine
and aqueous sodium bromide to produce bromine
and aqueous sodium chloride.
Cl2 (g)
+
NaBr(aq)

Br2(l)
+
NaCl(aq)
Notes:
• Chlorine and Bromine are a diatomic molecules
• Chlorine is normally a gas at room temperature
• Bromine is normally a liquid at room temperature
Write the equation for the reaction between solutions of aluminum
sulfate and calcium chloride to form a white precipitate of calcium
sulfate and aqueous aluminum chloride.
Al2(SO4)3(aq)
+
CaCl2(aq)

CaSO4(s)
+
AlCl3(aq)
Solid aluminum oxide is formed when aluminum metal
reacts with oxygen. Write the equation for this reaction.
Al (s)
+
O2 (g)

Al2O3 (s)
4 Al(s) + 3 O2(g)
2 Al2O3(s)
aluminum oxide
•The numbers in the front are called coefficients.
• Coefficients apply only to the element or compound that comes directly after it.
• Just like in math, a coefficient indicates that everything behind it is multiplied by
that number
4 Al = 4 aluminum atoms
• The numbers behind an atomic symbol are called subscripts
• Subscripts apply only to the element that comes directly before it
• If parenthesis come directly before the subscript, then the subscript is multiplied
by everything within the parenthesis
O2 = 2 oxygen atoms
(OH)2 = 2 oxygen atoms
2 hydrogen atoms
• Coefficients and subscripts together – multiply by both the coefficient and subscript
2(NH4)2 = 4 nitrogen atoms
16 hydrogen atoms
Chemical
Symbol
Meaning
Composition
H 2O
One molecule
of water:
Two H atoms and one O atom
2 H2O
Two molecules
of water:
Four H atoms and two O atoms
H 2 O2
One molecule
of hydrogen
peroxide:
Two H atoms and two O atoms
Law of Conservation of Matter
• Matter is not lost in a chemical reaction- Atoms are
just rearranged (Remember John Dalton?)
• The same atoms are present in a reaction at
the beginning (reactants) and at the end
(products)
• This means that when we write our chemical
equations, we need to have the same number of
atoms on both sides of the reaction arrow!
Otherwise matter would not be conserved.
Kotz web
H
Cl
Cl
Cl
H
H
Cl
H
H
Cl
Cl
Cl
H
H
H2(g) + Cl2(g)  HCl(aq)
reactants
H
Cl
(unbalanced)
H2(g) + Cl2(g)  2 HCl (aq) (balanced)
reactants
products
2
1
2
1
H
Cl
products
2
2
2
2
Balanced Equation – one in which the number of atoms
of each element as a reactant is equal to the number of
atoms of that element as a product
To balance equations, we add coefficients in front of the
element/compound
Do not change the subscripts because then you will
change the compound!
1. Identify the most complex substance.
2. Beginning with that substance, choose an element that
appears in only one reactant and one product.
• Adjust the coefficients to obtain the same number
of atoms of this element on both sides.
• Balance polyatomic ions as a unit (if possible).
• Re-write H2O as H-OH if hydroxide is present
3. Balance the remaining atoms
• End with the least-complex substance
• Leave single elements/diatomic molecules until last
4. Double check - Make sure that the atoms of each
element are the same on both sides of the equation.
CH4 (g) +
2
O2 (g)
CO2 (g) +
C=
H=
O=
Cl2 (g)
2
H2O (l)
C=
H=
O=
+ 2 NaBr(aq)

Br2(g)
2
NaCl(aq)
Cl =
Na =
Br =
Cl =
Na =
Br =
Al2(SO4)3(aq) +
+
3
Al =
SO4 =
Ca =
Cl =
CaCl2(aq)

3
CaSO4(s) +
Al =
SO4 =
Ca =
Cl =
2
AlCl3(aq)
Now you try…
2 (NH4)3PO4 + 3 Mg(OH)2  Mg3(PO4)2
2 AlCl3
+ 3 Li2CO3

Al2(CO3)3
+
6 NH4OH
+
6 LiCl