Counting Atoms and Counting Atoms and Balancing Chemical Balancing Chemical

EquationsEquations

Identifying CompoundsIdentifying Compounds

Each new element is identified by a capital Each new element is identified by a capital letterletter

Example: Example: HH22SOSO44

The elements in Sulfuric Acid The elements in Sulfuric Acid HydrogenHydrogenSulfurSulfurOxygenOxygen

SubscriptsSubscripts

CC1212HH2222OO1111

There are 12 atoms of CarbonThere are 12 atoms of CarbonThere are 22 atoms of HydrogenThere are 22 atoms of HydrogenThere are 11 atoms of OxygenThere are 11 atoms of Oxygen

If there is not a subscript listed, it is If there is not a subscript listed, it is understood to be 1.understood to be 1.

Example: Example: NaClNaClThere is one atom of SodiumThere is one atom of SodiumThere is one atom of ChlorineThere is one atom of Chlorine

You Practice!You Practice!

NaHCONaHCO33

Sodium – 1Sodium – 1

Hydrogen – 1Hydrogen – 1

Carbon – 1Carbon – 1

Oxygen -3Oxygen -3

HClHClHydrogen – 1Hydrogen – 1

Chlorine - 1Chlorine - 1

There are times you will see a compound There are times you will see a compound with parenthesis.with parenthesis.

Pb(NOPb(NO33))22

The 2 after the parenthesis indicates there The 2 after the parenthesis indicates there are two sets of the parenthesis. are two sets of the parenthesis.

Pb(NOPb(NO33) (NO) (NO33))

So, in counting the atoms, you would have So, in counting the atoms, you would have the following:the following:

Lead – 1Lead – 1 Oxygen - 6Oxygen - 6

Nitrogen -2Nitrogen -2

You Practice!!You Practice!!

(NH(NH44))33POPO44

Nitrogen – 3Nitrogen – 3

Hydrogen – 12Hydrogen – 12

Phosphorus – 1Phosphorus – 1

Oxygen – 4Oxygen – 4

Mg(OH)Mg(OH)22

Magnesium – 1Magnesium – 1

Oxygen – 2Oxygen – 2

Hydrogen – 2Hydrogen – 2

CoefficientCoefficient2H2H22SOSO44

This means there are 2 compounds of This means there are 2 compounds of Sulfuric Acid. Think:Sulfuric Acid. Think:

HH22SOSO44 HH22SOSO44

Counting the atoms:Counting the atoms:

Hydrogen – 4Hydrogen – 4

Sulfur – 2Sulfur – 2

Oxygen - 8Oxygen - 8

You Practice!!You Practice!!

3H3H33POPO44

Hydrogen – 9Hydrogen – 9

Phosphorus – 3Phosphorus – 3

Oxygen - 12Oxygen - 12

2H2H22OO

Hydrogen – 4Hydrogen – 4

Oxygen - 2Oxygen - 2

Got It????Got It????

Chemical EquationsChemical Equations

Chemical equations express what is Chemical equations express what is happening in a chemical reaction using happening in a chemical reaction using symbols.symbols.

2K + Cl2K + Cl22 2KCl2KCl

ReactantReactant ProductProduct

yieldsyields

Law of Conservation of MassLaw of Conservation of Mass

In a chemical reaction, matter In a chemical reaction, matter cannot be created or destroyed. cannot be created or destroyed. It can only be changed.It can only be changed.

Therefore the Reactants must Therefore the Reactants must equal the Products for the equal the Products for the equation to be balancedequation to be balanced

What does that mean??What does that mean??

The reactants MUST contain the The reactants MUST contain the same elements and the same same elements and the same number of each element as the number of each element as the product. product. BUTBUT they CAN be in they CAN be in different compounds.different compounds.

HUH?????HUH?????

HH22 + O + O22 HH22O O

ReactantsReactants ProductsProductsH = 2H = 2 H = 2H = 2O = 2O = 2 O = 1O = 1

This cannot happen. An oxygen atom This cannot happen. An oxygen atom cannot be destroyed.cannot be destroyed.

So what do we do?So what do we do?

The chemical equation must be written according The chemical equation must be written according to the law.to the law.

AGAIN --- HUH???AGAIN --- HUH???HH22 + O + O22 HH22O is the production of water. O is the production of water.

Well, how it actually happens in nature is this….Well, how it actually happens in nature is this….

2H2H22 + O + O22 2H2H22OOReactants: Reactants: Products: Products: H = 4 H = 4 H = 4 H = 4O = 2O = 2 O = 2O = 2

Do I Need to Know How to Do I Need to Know How to Balance?Balance?

NOT YET. You need to be able to NOT YET. You need to be able to recognize if the chemical reaction follows recognize if the chemical reaction follows the law of conservation of mass.the law of conservation of mass.

Na + ONa + O22 NaNa22O O

Mg + 2HCl MgClMg + 2HCl MgCl22 + H + H2 2

NOPE

YUP!!

You Practice!!!You Practice!!!

HgO Hg + OHgO Hg + O22

Hg = Hg = Hg = Hg =

O =O = O = O =

NN22 + 3H + 3H22 2NH2NH33

Zn + 2HClZn + 2HCl ZnCl ZnCl22 + H + H22

NOPE

YUP

YUP

More PracticeMore Practice

K + BrK + Br22 2KBr 2KBr

2Fe + O2Fe + O22 6Fe 6Fe22OO33

2Na + 2H2Na + 2H22OO 2NaOH + H2NaOH + H22

NOPE

NOPE

YUP

Got It???Got It???

Balancing Chemical EquationsBalancing Chemical Equations

HH22 + O + O22 HH22O O

Reactants: H = 2Reactants: H = 2 Products: H = 2 Products: H = 2

O = 2O = 2 O = 1 O = 1

What do we multiply by 1 to get 2?What do we multiply by 1 to get 2?

Keep Going….Keep Going….

HH22 + O + O22 22HH22O O

Reactants: H = 2Reactants: H = 2 Products: H = 4 Products: H = 4 O = 2O = 2 O = O = 22

Now the Oxygen is balanced but Hydrogen is Now the Oxygen is balanced but Hydrogen is not, so what do we multiply by 2 to get 4?not, so what do we multiply by 2 to get 4?

Almost There!!!Almost There!!!

22HH22 + O + O22 2H2H22O O

Reactants: H = Reactants: H = 44 Products: H = 4 Products: H = 4

O = 2O = 2 O = 2 O = 2

Now it is balanced!!! Congratulations, you Now it is balanced!!! Congratulations, you have now learned the hardest thing we will have now learned the hardest thing we will do all year!!do all year!!