C HEMICAL R EACTIONS

C HEMICAL C HANGES 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 (solid appears) Release of energy (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

C HEMICAL R EACTIONS 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)

L AW OF C ONSERVATION OF M ATTER 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 H 2 O 3 H = O = 4 Fe 2 O 3 Fe = O = 6 NaClNa = Cl = NO 2 N = O = Now let’s practice some harder stuff… WS – How many of each atom are there!

B ALANCED E QUATIONS In order to conserve atoms, you must balance the number and type of atoms on the reactants and products side of the equation

H OW 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 – gas s – solid l – liquid aq—aqueous solution

TAKE A LOOK AT THIS… Does it look balanced?

Is this balanced now? WE MUST THE GET THE O 2 TO BALANCE..

AND NOW….IS IT BALANCED? YES!

B ALANCED E QUATIONS 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!

S TEPS TO B ALANCING 1. Count the number and type of each type of atom on both sides 2. 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 + O 2 MgO Lets make a T-Chart to help us balance the sides…

LET’S TRY SOME TOGETHER Magnesium + Oxygen (gas) Magnesium Oxide Mg + O 2 MgO 1 Mg 1 2 O 1

LET’S TRY SOME TOGETHER Magnesium + Oxygen (gas) Magnesium Oxide Mg + O 2 2MgO 1 Mg 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 + O 2 2MgO 2 1 Mg O 1 2 Now balance out the Mg on the reactant side

LET’S TRY SOME TOGETHER Magnesium + Oxygen (gas) Magnesium Oxide 2Mg + O 2 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 + __Cl 2 __CCl 4 __Al 2 O 3 __Al + __O 2