CHEMICAL
REACTIONS
How do chemicals react with each other?
Chapter 23
WHAT IS A CHEMICAL REACTION?

Atoms change identity


A change of color is almost always present


Cold packs, light sticks
Usually gas is given off


Cu replaces Ag and turns solution blue
All chemical reactions give or use energy


Mg atom becomes Mg+2
Form bubbles
Precipitate is formed

Like a snow globe, flakes of a solid
 Any
of these signs indicates a
reaction.
WHY DO THEY OCCUR?
 Chemical
reactions occur between
atoms in order to form a bond
 Bonds form in order to complete the
outermost energy shell and become
less reactive, ions
CHEMICAL REACTIONS
A chemical reaction is an expression in which
symbols and formulas are use to represent a
chemical reaction.
 Reactants are written on the left, and products
are written on the right side of the yield sign ()


There are some equations that are written to
express reactions that never complete, they use
reversible arrows
CHEMICAL REACTIONS (RXNS)
 Begin
with reactants and end with
products
 Reactants
--- Products
 A + B  AB
 We
aren’t creating or destroying
atoms, only rearranging them
(Law of Conservation of Mass)
RATE OF CHEMICAL REACTIONS
The rate of a chemical reaction is a measure of
how quickly reactants turn into products
 Increasing these factors will increase the rate of
reaction:
 A catalyst is a substance that increases the
reaction rate of a reaction without itself being
changed by the reaction, Ex) enzymes


Speeds up and slows down a reaction
EXAMPLE
 Isooctane,
C8H18 and oxygen, O2
react to form CO2, carbon dioxide
and H2O, water
 C8H18 + O2  CO2 + H2O + Energy
KEY WORDS
 React with, combine with, and
+
 To form, yields, forms, produces, creates


 It
takes energy to break a bond (heat,
electric, sound, light) – can all transfer
energy
 Forming bonds releases energy

Both result in either a endothermic or exothermic
reaction
ENERGY CLASSIFICATIONS
Endothermic

Energy is absorbed
from surroundings
Exothermic

Energy is given off
from rxn
ACTIVATION ENERGY
The
energy required to start
a reaction
CHEMICAL ENERGY
 Energy
stored in chemical bonds
 Released with a reaction

Ex) bonds in coal store energy that is released
CHEMICAL REACTION TYPES
 Synthesis
– at least two substances form a new,
more complex compound
 Always combine substances to
form more complex substances
 Ex) A + B + C  ABC
 Ex) Na + Cl2  NaCl
 Decomposition
-
Complex compound breaks down into
simpler compounds
-
Ex) DeFG  DeG + F
Ex) 2H2O  2H2 + O2 (electrolysis of
water)
 Combustion
-
-
-
Uses oxygen as a reactant and products
will contain oxygen somewhere, usually as
CO2
A reaction where a compound and oxygen
will burn
Ex) CH4 + O2  CO2 + H2O
Methane combines with oxygen and
activation energy to burn and produce
carbon dioxide and water with light/heat
 Single
-
-
-
Displacement
Reaction in which one element will
replace atoms of another element in a
compound (especially within the same
family)
More reactive elements will take the place
of less reactive ones
Ex) 3CuCl2 + 2Al  2AlCl3 + 3Cu
Copper chloride combines with aluminum
to produce aluminum chloride and copper
ions
-
The aluminum replaced the copper
 Double
-
-
-
Displacement
Two compounds exchange ions (they
swap partners)
Ex) Pb(NO3)2 + K2CrO4  PbCrO4 +
2KNO3
Lead nitrate combines with potassium
chromate to form lead chromate and
potassium nitrate.
REDUCTION/OXIDATION REACTION
(REDOX RXN )
A reaction that occurs when electrons are
transferred between reactants
 One or more reactants is reduced and one or
more is oxidized

Reduced- substances that accept e Oxidized- substances that give up e

OIL RIG: Oxidation Is Loss; Reduction Is Gain
• OR

LEO says GER: Loss of Electrons is Oxidation
and Gain of Electrons is Reduction
SUMMARY OF RXN TYPES

Synthesis


Decomposition


AB + O2  A + BO2
Single Displacement


DEF  D + E + F
Combustion


A + B  AB
XA + B  BA + X
Double Displacement

AX + BY  AY + BX