BALANCING CHEMICAL BALANCING CHEMICAL EQUATIONSEQUATIONS

Chapter 6.5Chapter 6.5

DAY 1 & 2DAY 1 & 2

Word equations or formula (skeleton) Word equations or formula (skeleton)

equations need to be balanced.equations need to be balanced.

The number of atoms of one element The number of atoms of one element on the reactant side of an equation on the reactant side of an equation must equal the number of atoms of must equal the number of atoms of that same element on the product that same element on the product side of an equation.side of an equation.

LAW OF CONSERVATION OF MASSLAW OF CONSERVATION OF MASS

States: the total mass of atoms must States: the total mass of atoms must be the same on both sides of an be the same on both sides of an equation.equation.

Meaning –> the mass of the reactants Meaning –> the mass of the reactants equals the mass of the products.equals the mass of the products.

The same total number of each atom = The same total number of each atom = same total atomic masssame total atomic mass

How to count atoms reviewHow to count atoms review

Using Black line 6.5a, we will review Using Black line 6.5a, we will review counting atoms before we learn the counting atoms before we learn the skill of balancing equations.skill of balancing equations.

1) The 1) The symbolsymbol of an element of an element represents one atom of that elementrepresents one atom of that element

Example: Ca = 1 atomExample: Ca = 1 atom

2) A 2) A subscript subscript is a number written at is a number written at the the lower right cornerlower right corner after the after the symbol of an element. If there is symbol of an element. If there is more than one atom of the element more than one atom of the element in the molecule, then a subscript is in the molecule, then a subscript is used to indicate the number of used to indicate the number of atoms.atoms.

Example: NExample: N22 = 2 atoms = 2 atoms

3) A 3) A subscript outside a bracketsubscript outside a bracket

multiplies multiplies allall the elements the elements insideinside the the brackets.brackets.

Example: BaExample: Ba33(PO(PO44))22

Barium – 3 atomsBarium – 3 atoms

Phosphorus – 2 atomsPhosphorus – 2 atoms

Oxygen – 8 atomsOxygen – 8 atoms

4a) A 4a) A coefficientcoefficient is a number written is a number written in front of a chemical symbol and indicates a chemical symbol and indicates the number of atoms of that element.the number of atoms of that element.

Example: Example: 33C = 3 carbonsC = 3 carbons

4b) A 4b) A coefficientcoefficient is a number written is a number written in front of a chemical formula and indicates a chemical formula and indicates the number of molecules of that compound.the number of molecules of that compound.

22HH22O =O = Hydrogen 2 x Hydrogen 2 x 22 = 4 atoms, Oxygen 1 x = 4 atoms, Oxygen 1 x 22 = atoms = atoms

NOTE: A NOTE: A coefficient coefficient multiplies the number of multiplies the number of atoms of each element in the formula.atoms of each element in the formula.

44Cu(NOCu(NO33))22 = =

Copper 1 x Copper 1 x 44 = atoms, = atoms,

Nitrogen 1 x 2 x Nitrogen 1 x 2 x 44 = 8 atoms, = 8 atoms,

Oxygen 3 x 2 x Oxygen 3 x 2 x 44 = 24 atoms = 24 atoms

LETS BALANCE EQUATIONSLETS BALANCE EQUATIONS

STEP 1 – Write the formula equation of STEP 1 – Write the formula equation of the reaction.the reaction.

Example: CHExample: CH44 + O + O22 CO CO22 + H + H22OO

STEP 2 – Count the number of atoms of STEP 2 – Count the number of atoms of each type on the reactants side and each type on the reactants side and on the products sideon the products side

reactants productsreactants products

O – 2 O - 3O – 2 O - 3

C – 1 C - 1C – 1 C - 1

H – 4 H – 2H – 4 H – 2

3) Multiply each of the formulas by an 3) Multiply each of the formulas by an appropriate coefficient to balance the appropriate coefficient to balance the numbers of atomsnumbers of atoms

CHCH44 + + 22 O O2 2 COCO22 + + 22 H H22OO

4) Count atoms on each side to verify. 4) Count atoms on each side to verify. reactants productsreactants products

O – 4 O - 4O – 4 O - 4 C – 1 C - 1C – 1 C - 1 H – 4 H – 4H – 4 H – 4

GROUP PRACTICEGROUP PRACTICE

1) hydrogen and oxygen produce 1) hydrogen and oxygen produce waterwater

2) calcium and chlorine make calcium 2) calcium and chlorine make calcium chloridechloride

3) aluminum and oxygen produce 3) aluminum and oxygen produce aluminum oxidealuminum oxide

4) copper and iron(III) oxide make iron 4) copper and iron(III) oxide make iron and copper(I) oxideand copper(I) oxide

HOMEWORKHOMEWORK

1. How to Count Atoms Review1. How to Count Atoms Review

2. PAGE 229 # 2, 3ade2. PAGE 229 # 2, 3ade

3. Balancing Equations Worksheet 3. Balancing Equations Worksheet