C HEMICAL R EACTIONS. C HEMICAL C HANGES The substances present at the beginning of the reaction are...

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