CHEMICAL REACTIONS
7.1 SKIP MOLES
True
False
Statement
Products are on the left, and yield reactants
on the right of a chemical equation
Law of conservation of mass says that matter
(elements) cannot be created or destroyed
When balancing equations you CAN change
the subscripts, but NOT the coefficients
Avogadro's number is 6.02 x 1023 which is
about a mole
Cu + O2
CuO
Is balanced
True
False
Chemical Reactions


Chemical reactions change substances into new
substances with new chemical and physical
properties
Ways to know a chemical reaction is occurring:
A
release of gas
 A color change
 Production of light and/or heat
 The production of a precipitate (solid)
Parts of Chemical Reactions

The Law of Conservation of Mass
 States
that no matter can be created nor destroyed in
a chemical reaction
#
on the left = # on the right
Two parts of a chemical reaction
 Reactants:
a substance or molecule that participates in
a chemical reaction
 Usually
 Products:
found on the left side of an equation
a substance that is formed in a chemical
reaction
 Usually
found on the right side of an equation
Parts of a chemical equation
Coefficient
Subscript
2 H2 + O2  2 H2O
Products

Reactants
Atoms are rearranged in chemical reactions to
make new substances by making or breaking
bonds.
Chemical Equations

Chemical equation:
A
representation of a chemical reaction that uses
symbols to show the relationship between the reactants
and products
CH4
+
O2

CO2
+
H2 O
 When
balancing a chemical reaction you
may add coefficients in front of the
compounds to balance the reaction, but you
may NOT change the subscripts.
 Changing
the subscripts changes the compound!!
 Subscripts
are determined by the valence electrons
(charges for ionic or sharing for covalent)
The subscripts tell
you how many
atoms of a
particular element
are in a compound.
The coefficient tells
you about the
quantity, or number,
of molecules of the
compound


1. Write the correct formula for
the reactants and the products.
2. Find the number of atoms for
each element on the left side.
Compare those against the
number of the atoms of the
same element on the right side.


3. Determine where to place
coefficients in front of formulas
so that the left side has the
same number of atoms as the
right side for EACH element
4. Check your answer to see if:
 The numbers of atoms on
both sides of the equation
are now balanced.
 The coefficients are in the
lowest possible whole
number ratios. (reduced)
Write the equation that describes the burning of
magnesium in air to form magnesium oxide.
Magnesium + Oxygen (air)  Magnesium Oxide
2 MgO
Mg
+
O2
2 1 Mg
1 Mg
2 1O
2O

Balanced!

Potassium metal reacts violently with water to produce
potassium hydroxide and hydrogen gas.
Potassium + Water  Potassium Hydroxide + Hydrogen Gas
Math Practice pg 195

1. Balance the production of hydrogen chloride
from hydrogen and chlorine
Math Practice

Balance
 H2O2
 Mg
H2O + O2
+ HCL
H2 +
MgCl2
Math Practice

Ethylene, C2H4 burns in the presence of oxygen to
produce carbon dioxide and water vapor. Balance.
Moles


(Mol) is the amount of
subatnce that contains
about 6.02 x 1023
particles of that
substance.
Called Avagardo’s #
 Usually
atoms, ions, or
molecules

Molar mass- mass of 1
mole of a substance
TYPES OF REACTIONS
Ch. 7.2
True
False
Statement
A synthesis reaction is when a compound
breaks down into 2 or more elements
In single replacement 1 pair switches places,
and usually has 2 compounds on both sides
Combustion reactions always yield heat, light
and water
Oxidation reactions gain electrons, while
reduction lose electrons
AB A + B
Is decomposition
True
False
Types of reactions

5 Types of Reactions
 Synthesis
 Single
 Double
 Decomposition
 Combustion
Synthesis

Synthesis Reaction: A reaction in which two or more
substances combine to form a new compound
A + B  AB
Example: 2Na + Cl2  2NaCl
Decomposition

Decomposition Reaction: A reaction in which a
single compound breaks down to form two or more
simpler compounds.
AB  A + B
Example: 2H2O  2H2 + O2
Single Displacement

Single-Displacement Reaction:
A
reaction in which one element or radical takes the
place of another element or radical in a compound
AX + B  BX
+ A
Example: 3 CuCl2 + 2Al  2AlCl3 + 3Cu
Double Displacement

Double-Displacement Reactions:
A
reaction in which a gas, solid, or a molecular
compound forms from the apparent exchange of atoms
or ions between two compounds
AX
+
BY  AY
+
BX
Pb(NO3)2 + K2CrO4  PbCrO4 + 2 K2 NO3
Combustion

Combustion Reaction:
The oxidation of an
organic compound in
which heat is released



Also known as “burning”
Always contain a
hydrocarbon and
oxygen from the air as
reactants
Always produce carbon
dioxide, water, and heat
CH4 + 2O2 → CO2 + 2H2O
+ heat
LEO says GER!!!

Electrons are
sometimes transferred
in chemical reactions
 These
reactions are
called oxidationreduction reactions
(REDOX reactions)
LEOLose Electrons = Oxidation

Oxidation
 Substances
that lose
electrons are oxidized

Reduction
 Substances
that accept
electrons are reduced
GERGain Electrons = Reduction
Oxidation or Reduction?
 Fe
changes to Fe2+
 Pb4+
F
changes to Pb2+
changes to F1-
 Cr2+
changes to Cr3+
 Mg2+
changes to Mg
oxidation
reduction
reduction
oxidation
reduction
ENERGY CHANGE AND
REACTION RATES
7.3/4
True
False
Statement
Endothermic releases energy/forms bonds,
while exothermic absorbs energy/breaks
bonds
Increasing temperature speeds up the reaction
rate
The smaller the surface area and
concentration, that faster the reaction rate
A catalyst is a substance that speeds up a
reaction without being consumed
Reaction rate, is the rate at which products
turn into reactants
True
False
Energy is released or absorbed
Endothermic Reaction


Absorbs energy
Energy is required to
break bonds
Exothermic Reaction


Releases energy
Energy is greater than
energy needed to
break bonds
Conservation of Energy


Energy is not created or destroyed in endothermic
and exothermic reactions
Total energy at beginning = total energy at end
Reaction Rate




Rate at which reactants change into products over
time
How fast reactants are being consumed
How fast the products are being formed
How fast energy is absorbed or released
Factors Affecting Reaction Rate

Temperature

in temp= in rate
 Faster

particles
in temp= in rate
 Slower
particles

Surface Area

in S.A= in rate
 More
collisions
Factors Affecting Reaction Rate

Stirring
collisions= in rate
 Ex: Washing machine


Concentration
#
of particles in a
given volume
 in conc.= in rate
 in pressure= in rate
 gases
Factors Affecting Reaction Rate

Catalyst
 Affects
substance
w/out being used up
 Speeds up reaction
 Written over yield
arrow
EQUILIBRIUM
Ch 7.5
True
False
Statement
Means an equation is reversible/at
equilibrium
Equilibrium means the forward and reverse
paths of the reaction take place at the same
rate
There are 3 types of equilibrium-chemical,
physical and atomic
La Chatelier said when a change is
introduced, the equation will do the opposite
Temperature, pressure, and concentration
affect equilibrium
True
False
Equilibrium

State in which the forward and reverse paths of
change take place at the same rate
 Physical
and Chemical
Types of Equilibrium
Physical

Opposing physical
change takes place at
the same time
Chemical

Opposing chemical
changes take place at
the same time
La Chatelier’s Principle

When a change is introduced to a system in
equilibrium, the equilibrium shifts in the direction
that relieves the change
Factors Affecting Equilibrium

Temperature

in temp will shift in the
direction that removes
heat from the system

Pressure

in pressure will shift in
the direction that
decreases the pressure
of the system
Factors Affecting Equilibrium

Concentration
 Equilibrium
will shift in
direction that produces
concentration