Transcript Chapter 7
Chapter 11
Chemical Reactions
Chemical Equation
Describes chemical reaction.
Chemical equation: reactants yield products
Reactants Products
Much easier to write symbols and formulas
instead of words
Examples
Solid Iron reacts with oxygen gas to form the solid
IronIIIoxide.
iron(s) + oxygen(g) ironIIIoxide(s)
Fe(s) + O2(g) Fe2O3(s)
Carbon tetrahydride gas BURNS to form carbon dioxide
gas and water vapor.
Carbon tetrahydride(g) + oxygen(g) carbon dioxide(↑) + water(↑)
CH4(g) + O2(g) CO2(↑) + H2O(↑)
Skeleton Equation: chemical equation that tells you what the
reactants and products are but NOT how much of each you have.
First step in writing a chemical equation.
Symbols Used
(s)
(l)
(g)
(↑)
(aq)
()
D
Pt
solid
liquid
gas
gas as a product
aqueous (in water solution)
ppt (precipitate) solid product from 2 aqueous
reactants
means with heat
means with Platinum catalyst: speeds up a
reaction without being used.
reversible reaction
Balancing Chemical Equations
Balanced equations have:
the same # of atoms of each element on
BOTH sides of the equation.
Law of Conservation of Mass – atoms can
neither be created nor destroyed, simply
rearranged.
Rules for Balancing Equations
Get the correct formulas for reactants and
products.
(USE ION CHART AND DON”T FORGET
DIATOMIC ELEMENTS!)
Write reactants on left, products on right.
Use plus signs to separate compounds and
yield sign to separate the reactants from
products.
Rules Continued
Count the # of atoms of each element in
reactants and products. (Polyatomic atoms
on both sides count as one.)
Balance # of each element using
coefficients.
Coefficient – small whole # in front of a
formula.
NEVER CHANGE FORMULA
SUBSCRIPTS
Rules for Balancing Equations
Balance elements appearing 3 or more
places LAST.
Check each element to make sure equation
is balanced.
Make sure all coefficients are in the lowest
whole number ratio.
Do not change subscripts!!!
Diatomic Molecules
Diatomic Molecules- a molecule made up two
atoms of the same element. They are only
diatomic when they are alone.
-There are 7 naturally occurring
diatomic molecules.
H O N Cl
Br
I F
Balancing Examples
___ C(s) + ___ O2(g) ___ CO2 (g)
___ C(s) + ___ O2(g) ___ CO (g)
___ AgNO3(aq) + ___Cu(s) ___ Cu(NO3)2(aq) + ___ Ag(s)
___ Al(s) + ___ O3(g) ___ Al2O3(s)
*___ C2H6(g) + ___ O2(g) ___ CO2(g) + ___ H2O(g)
*___ H3PO3 ___ H3PO4 + PH3
5 Types of Chemical Reactions
Combination Reaction – elements combine to
form a compound.
A
+B
AB
element + element compound
Ex. Sodium + chlorine sodium chloride
2
2 NaCl(s)
___Na(s)
+ ___ Cl2(g) ___
5 Types of Reactions
Decomposition Reaction – compound
breaks down into its element.
D
A+B
compound D element + element
AB
Ex: MercuryII oxide mercury + oxygen
2 HgO ___Hg
2
___
+ ___O2
5 Types of Reactions - 3
Single Replacement Reaction – one element
replaces another element in a compound.
+ -
+
+
AB + C
+ -
-
AB + D
+ -
A + CB
or
+ -
-
AD + B
Examples of Single Replacement
Reactions
• Must use Activity Series to see if reaction works
• Zinc + sulfuric acid zinc sulfate + hydorgen
• Zn(s) + H2SO4(aq) ZnSO4(aq) + H2(↑)
• Periodic table is activity series for halogens
•
Sodium bromide + chlorine sodium chloride + bromine
•
2
2
___NaBr(s)
+ ___Cl2(g) ___NaCl(s)
+ ___Br2(↑)
5 Types of Reactions
Double Replacement Reaction – two compounds react and
exchange positive ions to form two new compounds.
+ + + + -
AB + CD
AD + CB
Barium Chloride(aq) + potassium carbonate(aq)
barium carbonate() + potassium chloride(aq)
2 KCl(aq)
BaCl2(aq) + K2CO3(aq) BaCO3() + ___
5 Types of Reactions
Combustion Reaction – oxygen reacts with a
compound composed of C and H.
C x Hy + O 2
CO2 + H20
Also called Burning (exothermic)
The products are always CO2 and H2O.
Examples of Combustion Reactions
1.
C6H6 + 7½ O2
2 C6H6 + 15 O2
2.
CH3OH + 1½ O2
2 CH3OH + 3 O2
6 CO2 + 3 H2O
12 CO2 + 6 H2O
CO2 + 2 H2O
2 CO2 + 4 H2O
Special Decomposition Reactions:
Decomposition
of a Carbonate:
Metal carbonate metal oxide + carbon dioxide
XCO3
ex. Na2CO3
XO + CO2
Na2O + CO2
Special Decomposition Reactions:
Decomposition
of a Hydroxide:
Metal hydroxide metal oxide + water
XOH
ex. 2NaOH
XO + H2O
Na2O + H2O
Special Decomposition Reactions:
Decomposition
ex.
of a Chlorate: (ClO3)
Metal chlorate metal chloride + oxygen
XClO3
2
___NaClO
3
XCl + O2
___NaCl + ___O
3 2
Special Decomposition Reactions: 4
Special
single Replacement Reaction:
»Group IA or IIA metal and H2O
X + HOH
ex. 2Na + 2HOH
XOH + H2
2NaOH + H2
How to ID types of reactions.
Combination Reactions – given 2 items that form 1
new compound.
Decomposition Reactions – given a single
compound that breaks into parts.
Single Replacement – given a single element plus a
single compound, forms a new compound a a
different element.
Double Replacement – given two compounds (+’s
change places).
Combustion Reaction – given CH compound with
Oxygen, always forms water and carbon dioxide.