Download Chemical Reactions

CHEMICAL REACTIONS
CHEMICAL CHANGES
 The
substances present at the beginning of
the reaction are changed into something
new.

Essentially, you are going to break bonds,
rearrange those atoms, and form new
bonds.
CHEMICAL CHANGE – THINGS YOU REMEMBER…
Signs:


Bubbles of Gas
appear
A precipitate forms


Release of energy




(solid appears)
(The temperature changes)
A color Change
Burning something
There is a different
smell
Examples:
 Gasoline
is ignited
 Car rusting
 Milk goes sour
 Bread becomes toast
 A tree burning
 Hydrogen Peroxide
bubbles in a cut
 Photosynthesis
CHEMICAL REACTIONS
 All
chemical changes are results of
chemical reactions.
Happens when you make or break bonds
 Involves rearrangement of atoms

 One
set of compounds (reactants) forms
another set of compounds (products)
LAW OF CONSERVATION OF MATTER
 So
why are chemical equations, and balanced
chemical equations, so important?
 Matter cannot be created or destroyed, but
can only change forms
So when we write equations…
 The number of each type of atom on the
reactants side must be equal to the number
of each type of atom on the products side

# of atoms of REACTANTS = # of atoms of
PRODUCTS
BEFORE WE CAN BALANCE…

We need to be able to look at one side of the equation
Coefficient: Tells
us how many of
that entire
molecule we have
Subscript: Tells
us how many of
that one single
atom we have
BEFORE WE CAN BALANCE…

How many do you have of each?

2 H2O3
H=
O=

4 Fe2O3
Fe =
O=

6 NaCl
Na =
Cl =

NO2
N=
O=
 Now

let’s practice some harder stuff…
WS – How many of each atom are there!
BALANCED EQUATIONS
 In
order to conserve atoms, you must
balance the number and type of atoms on
the reactants and products side of the
equation
HOW DO WE WRITE CHEMICAL
REACTIONS?
 Reactants
 Symbols
on the left, products on the right
show what is happening
+ (plus, added to, mixed with)
  (forms, produces, yields)
 g – gas
 s – solid
 l – liquid
 aq—aqueous solution

TAKE A LOOK AT THIS…

Does it look balanced?
WE MUST THE GET THE O2 TO
BALANCE..

Is this balanced now?
AND NOW….IS IT BALANCED?
YES!
BALANCED EQUATIONS

When balancing equations, you are not allowed to
change the chemical composition.


you CAN’T CHANGE SUBSCRIPTS!
Can only change the numbers of molecules (or atoms)
on each side of the equation.

you CAN ADD COEFFICIENTS!
STEPS TO BALANCING
1.
2.
3.
Count the number and type of each type of atom
on both sides
If there are different numbers of atoms on each
side, you must add coefficients to compounds
to change the number of atoms
Figure out what number to multiply each
compound by in order to make the numbers of
atoms add up
 Remember: you can never change the
compound, you can only add coefficients.
LET’S TRY SOME TOGETHER
 Magnesium
+ Oxygen (gas)
Magnesium
Oxide
Mg + O2
MgO
Lets make a T-Chart to help
us balance the sides…
LET’S TRY SOME TOGETHER
 Magnesium
+ Oxygen (gas)
Magnesium
Oxide
Mg + O2
1 Mg 1
2 O 1
MgO
LET’S TRY SOME TOGETHER
 Magnesium
+ Oxygen (gas)
Magnesium
Oxide
Mg + O2
2MgO
1 Mg 1 2
2 O 1 2
Add a coefficient of 2 to MgO and change your chart…
LET’S TRY SOME TOGETHER
 Magnesium
+ Oxygen (gas)
Magnesium
Oxide
2Mg + O2
2MgO
2 1 Mg 1 2
2 O 1 2
Now balance out the Mg on the reactant side
LET’S TRY SOME TOGETHER
 Magnesium
+ Oxygen (gas)
Magnesium
Oxide
2Mg + O2
2MgO
Annnnd done. We have a coefficient of 2 in front
of the reactant Mg and the product MgO.
Use your T-Chart. It will make balancing much
easier.
NOW TRY ON YOUR OWN…

__C + __Cl2

__Al2O3
__CCl4
__Al + __O2