Transcript Ch. 8 Notes (Chemical Reactions) Teacher 2010

•
Ch. 8 Notes -- Chemical Reactions
Chemical equations give information in two major areas:
Reactants
products
1. _____________
and ______________
of the reaction.
amount
2. Coefficients of a balanced chemical equation tell us the ______
of the substances involved.
Example of a Balanced Chemical Equation: 2H2 (g) + O2 (g)  2H2O (g)
left side of the arrow, and the
Reactants are on the ______
right
yields
products are on the __________
side. The arrow means “________”,
or “reacts to produce” when read aloud.
•
•
•
From our example, hydrogen reacts with oxygen in a ___:___
2 1 ratio.
moles or
The coefficients represent either the number of _________
molecules present.
The coefficients can also represent _________
liters if the substances are
gases.
(1 mole = 6.02 x 1023 molecules, 1 mole of gas= 22.4 Liters)
Common Symbols used in Chemical Equations
+
→
(See Table 8.1)
= used to separate 2 reactants or 2 products from each other
= “yields” or “reacts to produce”
= _____________
reaction (like a rechargeable battery)
reversible
(s) (l) (g) (aq) = phase of matter: (solid, liquid, gas, or “aqueous”)
heat
= ___________
supplied to the reaction
MnO2
= a catalyst, (in this case, MnO2), is used to ________
speed ____
up
the reaction.
Decoding Common Chemical Equation Symbols
Practice Problems: Describe the following reactions using complete
sentences.
a) NaHCO3 (s) + HCl (aq)  NaCl (aq) + H2O (l) + CO2 (g)
b) H2SO4 (aq) + BaCl2 (aq)  HCl (aq) + BaSO4 (s)
c) Write a chemical equation from the following description: “Sodium
plus bromine, when heated, reacts to produce solid sodium bromide.”
Balancing Chemical Equations
Why do you have to balance a chemical equation?
• Law of Conservation of Matter (or Mass):
“Matter is neither
____________
nor _______________
in chemical reactions.”
created
destroyed
joined
• During a chemical reaction, atoms are either _________,
______________,
or rearranged. The _____________
and type of
separated
number
each atom stays the same.
How do you balance a chemical equation?
• __________________
are placed in front of the substances involved
Coefficients
in the chemical reaction to get the same number of atoms of each
element on both sides of the equation. This number will multiply the
number of atoms there are in a formula.
Rules for Balancing Chemical Equations
(1) Coefficients can only be placed ___
in _________
front
of a chemical
formula.
Practice Problems: How many atoms of each type are indicated in
the following compounds?
24 P= ___
2 O= ___
8
H= ___
(a)
2 (NH4)3PO4
N= 6___
(b)
4 KC2H3O2
4 C= ___
8 H= ___
12 O= ___
8
K= ___
(c)
3 Ca(NO3)2
3 N= ___
18
6 O= ___
Ca= ___
Rules for Balancing Chemical Equations
(2) You cannot change a ________________!!
subscript
Example :
2 H2 +
O2  2 H2O
H2 O2
To balance oxygen, you cannot change water’s formula to_________!
(3) You cannot place the coefficient in the ______________
of a
middle
formula!!
Example :
2Al +
N2  2 AlN
To balance nitrogen, you cannot put a 2 in the middle to make _______.
Al2N
whole
# ratio.
(4) Reduce the coefficients to the simplest ____________
___
Example:
4H2 + 2O2  4H2O can be reduced to…
__H
2 2 + __O
1 2  __H
2 2O
Rules for Balancing Chemical Equations
(5) Get rid of any ____________!
Coefficients must be _________
fractions
whole #’s
• You can’t have a _______________
of a molecule or atom!
fraction
Example: 2 x ( 1H2 + ½O2  1H2O )
__
2 H2 + __O
1 2  __H
2 2O
changes to…
Balancing Equations: “Helpful Hints”
a) Balance elements that appear in more than one compound ________.
last
1
___(NH
4)2CO3 
2
___NH
3
+
1
___CO
2
+
1 2O
___H
ion “___________”
chunks
b) Balance _____
as though it were one item as long as
the ion stays together as a group on each side of the yields arrow.
2
3
___Al
+ ___CuSO
4 
1 2(SO4)3 +
___Al
3
___Cu
start _________
over and begin
c) If you can’t seem to get it balanced, _________
with a different element the next time, or put a “2” somewhere and
then try again.
2
2 2O
___Li
+ ___H

2
1 2
___LiOH
+ ___H
d) This is what I’ll constantly be telling you to do if you are stuck and
you need my help... “Pick an element to balance. How many are on
Fix
it
the left side? How many are on the right side? ________
____!”
2
___Fe(OH)
3 
1 2O3 + ___H
3 2O
___Fe
Balancing Equations: “Helpful Hints”
e) Mr. Reid’s goofy “balancing song” may help:
2 on the left and a ___on
3
3 on the
“If there’s a ___
the right, you put a ___
left and a ___
2 on the right, (makin’ money!)”
___Al
4
+ ___O
3 2  ___Al
2 2O3
f) If you see only C’s H’s and O’s, balance them in this order: C, H, O.
___C2H2 +
___O2 
___CO2
+
___H2O
___C
2 2H2 +
___O
5 2 
___CO
4
2
+
___H
2 2O
Six General Types of Reactions
1) ________________________:
Decomposition
•
one ______________
compound into simpler
A reaction that breaks apart ______
substances, (usually two elements or an element and a smaller
compound.)
+
General Form: _____
AX  ___
A + ___
X
H2 + _____
O2
Examples:
H O  _____
2
Remember that “HONClBrIF” elements are diatomic when alone!!
General Types of Reactions (Continued)
2) _______________:
Composition
(sometimes called “Combination” or “Synthesis”)
•
•
two __________________,
substances
A reaction of _____
typically a metal and a
nonmetal to form ______
one ______________.
compound
It is the opposite of decomposition. (The same categories of
reactions from above apply, just in reverse.)
+
General Form:
Examples:
A + ___
X  _____
AX
___
Al
+
Cl2  _______
AlCl3
2 elements
 binary compound
Pb(OH)2
PbO + H2O  ___
metallic + water 
oxide
hydroxide
General Types of Reactions (Continued)
3) _____________
Single
Replacement:
•
one ______________
compound
one ____________
element
A reaction between ____
and ___
that produces a different _____________
compound
and ______________.
element
General Forms: ____
AX + __
Y  ____
AY
+
+ __
X
AX
B  ____
BX + __
A
____ + __
+
•
•
•
•
more
The element that is trying to replace the other must be ________
reactive
_______________
than the one it is replacing.
You must use the Activity Series to see if the reaction will happen.
Table 8.2
_________
Higher ___
up = more reactive
Elements from ____
Li to ____
Na can displace hydrogen in water to
form a metallic hydroxide and H2 gas.
Activity Series
Single Replacement Reactions
Examples:
NaCl
NaF + _____
Cl2
+ F2  _____
FeCl2 +
KCl + _____
Fe
K  _____
HCl
+
H2
Zn  ZnCl
_____
2 + _____
HCl
+
No Reaction
Au  _____
+ _____
NaOH + _____
H2
H2O + Na  _____
H(OH)
CuNO3+ _____
Ag
AgNO3 + Cu  _____
General Types of Reactions (Continued)
4) _______________
Double
Replacement: (sometimes called “Ionic”)
•
•
two ________________
compounds
A reaction between _____
that are dissolved in
water that produces _____
two ________________
compounds
, one of which is
________________.
insoluble
Water or a gas may be one of the two compounds being produced.
BX(s)
(aq)+ BY
(aq)  AY
(aq) + ____
General Form: AX
____
____
____
+
•
•
+
You must use the Solubility Chart to see which product is the
precipitate.
Table A-7 on p.887
I or _____=
sS
___
precipitate
Examples: CaCl2 (aq) +
AgCl(s)
AgNO3 (aq)  Ca(NO
_________
3)2 (aq) + ________
NO REACTION
NaCl(aq)+ ________
H2O (l)
NaOH (aq) + HCl (aq)  ________
General Types of Reactions (Continued)
5) _________________:
Combustion
•
•
•
A reaction between a Carbon/Hydrogen (and sometimes Oxygen)
O2
_________________
compound
with _____.
CO2 + ________
H2O
The products are always the same… ________
This reaction is too easy!! Don’t miss it!
General Form:
Examples:
C2H2
CO2 + ____
H2O
CxHy + O2  ____
+
C7H6O +
CO2 + _______
H2O
O2  _______
CO2 + _______
H2O
O2  _______
General Types of Reactions (Continued)
6) _________________:
Nuclear
Fission and Fusion
• There are two types of Nuclear reactions, ________________
– Fission reactions involve a heavy nucleus that will split into two
or three pieces.
– Fusion reactions involve two light nuclei that combine into a
heavier one.
• You will not be asked to predict products!
• Examples of nuclear reactions:
Nuclear Weapons
Fission
General Types of Reactions (Continued)
6) _________________:
Nuclear
• Examples of nuclear reactions:
Nuclear Medicine /Medical Imaging
Fission
Nuclear Power
Fission
General Types of Reactions (Continued)
6) _________________:
Nuclear
• Examples of nuclear reactions:
Two Hydrogen on
the sun become
Helium
Fusion