CHEMICAL
EQUATIONS
1
Water and what is known from its
equation.
2H2
+ O2
→ 2H2O
hydrogen
+
oxygen
→ water
4 atoms H
+
2 atoms O
→ 4 atoms H +
2 atoms O
1 molecule O
→
2 molecules H
+
2 molecules water
2 moles H
+
1 mole O
→ 2 moles water ***
4 amu H
+
32 amu O
→
36 amu water
4 grams H
+
32 grams O
→
36 grams water
2
*** Note that molecules and moles always have the SAME RATIOS
CHEMICAL REACTIONS


one or more substances are changed
into different substances
Represented by chemical equations
• 2H2 (g) + O2(g)

REACTANTS

2H2O(g)
PRODUCTS 
3
CHEMICAL EQUATIONS



Show the substances undergoing
change and the result(s).
Show relative amts. of
elements/cmpds. that take part in
the changes [coefficients]
See ‘Symbols Used in Chem. Rxn.
handout
4
11.1
Writing Chemical Equations
5
6
11.1
Writing Chemical Equations

iron + oxygen  iron(III) oxide
7
11.1
Writing Chemical Equations

Hydrogen Peroxide  Water and Oxygen
8
The PVC Method
to WRITING A BALANCED CHEMICAL EQUATION
•Pair the elements
properly
•Valences give subscripts
•Coefficients balance
the equation
9
WRITING A BALANCED
CHEMICAL EQUATION



Tips:
Start with element that appears only once
on each side.
Save oxygen and hydrogen for last
10
Lithium aluminum hydride reacts with water to
produce lithium hydroxide, aluminum
hydroxide and hydrogen gas.




LiAlH4 + H2O  LiOH + Al(OH)3 + H2
LiAlH4 + 4H2O  LiOH + Al(OH)3 +
H2
LiAlH4 + 4H2O  LiOH + Al(OH)3 +
4H2
*Note that hydrogen is diatomic when not
bonded to other elements.
11
Diatomic Molecules
Harvey BrOFINCl
12
Persistent difficulty ?

Check all FORMULAS to make sure
they are correct
•K2(SO4) v K2(SO3)
13
Ammonia reacts with oxygen gas to
produce nitrogen dioxide and
water.





NH3 + O2  NO2 + H2O
2NH3 + O2  NO2 + 3H2O
2NH3 + O2  2NO2 + 3H2O
2NH3 + 7/2O2  2NO2 + 3H2O
4NH3 + 7O2
 4NO2 + 6H2O
14
Synthesis
15
Common Types of Chemical
Reactions



Synthesis
two or more simple compounds
combine to form a more complicated
one
General form : A + B ---> AB
Iron and sulfur to form iron (II)
sulfide:
8 Fe + S8 ---> 8 FeS
16
Decomposition
17
Common Types of Chemical
Reactions




Decomposition
opposite of a synthesis reaction
complex molecule breaks down to
make simpler ones
General form: AB ---> A + B
Hydrogen peroxide decomposes to water and
oxygen gas:
H2O2  H2O +O2
18
Single Replacement
19
Common Types of Chemical
Reactions



Single Replacement
one element trades places with
another element in a compound
General form: A++ BC ---> AC + B,
or
A- + BC ---> BA + C
Zinc replaces copper in copper sulfide solution:
Zn + CuSO4  ZnSO4 + Cu
20
Double Replacement
21
Common Types of Chemical
Reactions
Double Replacement


cations (positive ions) of two different
molecules switch places, forming two
entirely different compounds
General form:
AB + CD ---> AD + CB

Sodium Chloride (salt) solution reacts with silver
nitrate to produce silver chloride and sodium
nitrate.
NaCl +AgNO3  AgCl + NaNO3
22
23
Common Types of Chemical
Reactions
Combustion





oxygen combines with a compound
containing carbon, hydrogen and
sometimes oxygen
forms water and carbon dioxide.
General Form: CxHy  CO2 + H2O
Exothermic
Burning of naphthalene:
C10H8 + 12 O2 ---> 10 CO2 + 4 H2O
24
Review and Foreshadow

Video
• Logic and rules for balancing chemical
equations are reviewed
• Types of chemical reactions are
introduced


Take Notes
Quiz (10 points) @ end of video
• Name
• Period
• Number 1-10
25
Decomposition: Special
Cases


Anions and cations do not separate
as expected.
X = any metal
26
Metal carbonates



XCO3  XO + CO2
metal oxide & carbon dioxide
CaCO3  CaO
+
CO2
27
Metal hydroxides



XOH

XO + H2O
metal oxide & water
Ca(OH)2 
CaO
+
H2O
28
Metal chlorates



XClO3  XCl
+ O2
metal chloride & oxygen gas
Ca(ClO3)2  CaCl2
+
3O2
29
Single Replacement
Reactions




A++ BC ---> AC + B, or
A- + BC ---> BA + C
Are the free elements always able to
replace the element in the
compound?
How can we tell when / if the free
elements will successfully replace the
element in the compound?
30
Activity Series [partial listing]
Metals
lithium
potassium
Decreasing
Activity
↓
↓
Halogens
fluorine
chlorine
calcium
sodium
↓
↓
bromine
oxygen
magnesium
aluminum
zinc
↓
↓
↓
iodine
sulfur
chromium
iron
↓
↓
31
Will these reactions occur?




ZnCO3 + H2 ?
ZnCO3 + H2 N.R.
AgCl + Mg ?
2AgCl + Mg MgCl2 + 2Ag
32
Replacing HYDROGEN in WATER


Water is unusually stable.
Replacing the hydrogen in water depends
on:
• Placement of free element on activity
series, and
• TEMPERATURE
33
Replacing HYDROGEN in WATER
• < 175 oC

X
+
H 2O


Ca +
 XOH
+
H2
Metal hydroxide hydrogen gas
2H2O  Ca(OH)2
+ H2
• > 175oC

X
+
H 2O
Ca +
H2O


 XO
+
H2
Metal oxide hydrogen gas
 CaO + H2
34
Double Replacement
Reactions


AB + CD ---> AD + CB
When a double replacement
reaction occurs one of the
following are produced:
• gas
• precipitate

an insoluble solid that forms when two
liquids are mixed
• water

These rxn also called acid-base rxn
35
SOLUBILITY

The property of a substance to
dissolve
• Water
• Universal solvent




Solubility Table - handout
NaCl + AgNO3  NaNO3 + AgCl
2NaCl + Fe(NO3)2  2NaNO3 + FeCl2
 NR (no double replacement
products made)
36
Predicting Reaction Products




Analyze the reactants.
Decide what pattern of chemical
reaction the reactants will fit.
Na and H2SO4
• a single element and a compound fit the
single replacement pattern.
H2 and O2
• two elements fit the synthesis pattern.
37
Use the pattern to decide which
elements will go together.


[REMEMBER to refer to the Activity Series for
single replacement reactions.]
Na + H2SO4 →
• Na replaces H [Na stronger than H]; H
becomes lone element.
• 2Na + H2SO4 → Na2SO4 + H2
38
Use valences to form good chemical
formulas to represent the products.



The sum of the valences equals zero in a
chemical formula.
Na+1; SO4-2
• 2Na + H2SO4 → Na2SO4 + H2
Write the diatomic elements as H2, Br2,
O2, F2, I2, N2, and Cl2. when they are by
themselves.. (Henry BrOFINCl)
• 2H2 + O2 → 2H2O
39
Balance the equations using
coefficients
(BIG numbers placed in FRONT of the chemical formula.)

2Na + H2SO4 → Na2SO4 + H2
2H2 + O2 → 2H2O

Balance H, O last.

40
Nuclear Equations

Nuclear equations result in the
change of one element into another
transmutation
• 238
number of protons + neutrons
92
U number of protons
(determines identity of
atom)
41
42
α particle decay

238
92

234
U

Th +
thorium
90
4
2He
α particle
43
β particle decay

234
90


234
Th  91 Pa +
protactinium
0
-1eβ particle
Decay continues until a stable
substance is reached.
44
K capture decay

100
46
0
Pd
+
-1e- 
100
45
Rh
45
Rules for balancing nuclear
equations


The sum of the mass numbers (top)
is the same on both sides of the
equation.
The sum of the electric charges
(bottom) is the same on both sides
of the equation.
46
Find the unknown product





18
9F 
0
+1 e-
+
?
Find the mass
18 = 0 + x
18 = x
18
9F 
+
0
1e-
18
+
?
47
230?V X




Find the charge
9 = 1 + x
8 = x
18
9F 
0
+1e-
+
18
8?
48

Find the element

18
9
0
F 
+1
18
e-
+
8
O
49