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CHEMICAL REACTIONS
CHEMICAL CHANGESThe 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
appearA precipitate forms
(solid appears)
Release of energy (The temperature changes)
A color ChangeBurning somethingThere 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 REACTIONSAll chemical changes are results of
chemical reactions.Happens when you make or break bondsInvolves 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 atoms 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
Subscript: Tells us how many of that one single atom we have
Coefficient: Tells us how many of that entire molecule 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 EQUATIONSIn 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 on the left, products on the right
Symbols show what is happening+ (plus, added to, mixed with) (forms, produces, yields)
g – gass – solidl – liquidaq—aqueous solution
TAKE A LOOK AT THIS…
Does it look balanced?
Is this balanced now?
WE MUST THE GET THE O2 TO BALANCE..
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 BALANCING1. Count the number and type of each type of
atom on both sides2. If there are different numbers of atoms on
each side, you must add coefficients to compounds to change the number of atoms
3. 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 MgO
1 Mg 1 2 O 1
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 __CCl4
__Al2O3 __Al + __O2