CHEMICAL EQUATIONS - Derry Area School District
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Transcript CHEMICAL EQUATIONS - Derry Area School District
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