Balancing Balancing Chemical Chemical EquationsEquations

Balanced EquationBalanced Equation Atoms can’t be created or destroyedAtoms can’t be created or destroyedLaw of Conservation of Law of Conservation of MassMass

All the atoms we start with we must end All the atoms we start with we must end up withup with

A balanced equation has the same A balanced equation has the same number of each element on both sides of number of each element on both sides of the equation (reactant and product sides).the equation (reactant and product sides).

Counting AtomsCounting Atoms 2H2H22 + O + O2 2 2H 2H22OO

ReactantsReactants productproduct

SubscriptSubscript: (numbers below): (numbers below) indicates how many atoms of an element.indicates how many atoms of an element.

Coefficient Coefficient (numbers in front)(numbers in front) Indicates how many molecules/moles of a Indicates how many molecules/moles of a

compoundcompound ((multipliesmultiplies the number of atoms of each element the number of atoms of each element

in the compound)in the compound)

Chemical FormulaCounting up

Atoms

Let’s PracticeLet’s Practice NHNH33

_____ atoms of Nitrogen_____ atoms of Nitrogen _____ atoms of Hydrogen_____ atoms of Hydrogen _____ molecules/moles of NH_____ molecules/moles of NH33

NaClNaCl _____ atoms of Sodium_____ atoms of Sodium _____ atoms of Chlorine_____ atoms of Chlorine _____ molecule/moles of NaCl_____ molecule/moles of NaCl

PracticePractice NHNH33

__1___ atoms of Nitrogen__1___ atoms of Nitrogen __3___ atoms of Hydrogen__3___ atoms of Hydrogen __1__ molecules/moles of NH__1__ molecules/moles of NH33

NaClNaCl __1___ atoms of Sodium__1___ atoms of Sodium __1___ atoms of Chlorine__1___ atoms of Chlorine __1___ molecule/moles of NaCl__1___ molecule/moles of NaCl

Practice AgainPractice Again 8NaCl8NaCl

_____ atoms of Sodium_____ atoms of Sodium _____ atoms of Chlorine_____ atoms of Chlorine _____ molecule/moles of NaCl_____ molecule/moles of NaCl

3NH3NH33 ____ atoms of Nitrogen____ atoms of Nitrogen ____ atoms of Hydrogen____ atoms of Hydrogen ___ molecule/moles of NH___ molecule/moles of NH33

Ca(NOCa(NO33))22 _____ atoms of Calcium_____ atoms of Calcium _____ atoms of Nitrogen_____ atoms of Nitrogen _____ atoms of Oxygen_____ atoms of Oxygen _____molecule/moles of Ca(NO_____molecule/moles of Ca(NO33))22

Practice AgainPractice Again 8NaCl8NaCl

__8___ atoms of Sodium__8___ atoms of Sodium __8___ atoms of Chlorine__8___ atoms of Chlorine __8___ molecule/moles of NaCl__8___ molecule/moles of NaCl

3NH3NH33 __3__ atoms of Nitrogen__3__ atoms of Nitrogen __9__ atoms of Hydrogen__9__ atoms of Hydrogen __3_ molecules/moles of NH__3_ molecules/moles of NH33

Ca(NOCa(NO33))22 ___1__ atoms of Calcium___1__ atoms of Calcium ___2__ atoms of Nitrogen___2__ atoms of Nitrogen ___6__ atoms of Oxygen___6__ atoms of Oxygen ___1__molecule/moles of Ca(NO___1__molecule/moles of Ca(NO33))22 What if there is a coefficient of 2 in front of Ca(NOWhat if there is a coefficient of 2 in front of Ca(NO33))2 2 ??

More PracticeMore Practice SOSO22 + 3H + 3H22OO

_____ atoms of Sulfur_____ atoms of Sulfur _____ atoms of Hydrogen_____ atoms of Hydrogen _____ atoms of Oxygen_____ atoms of Oxygen _____ molecule/moles of SO_____ molecule/moles of SO22

_____ molecules of H_____ molecules of H22OO

More PracticeMore Practice SOSO22 + 3H + 3H22OO

__1___ atoms of Sulfur__1___ atoms of Sulfur __6___ atoms of Hydrogen__6___ atoms of Hydrogen __5___ atoms of Oxygen__5___ atoms of Oxygen __1___ molecule/moles of SO__1___ molecule/moles of SO22

__3___ molecules of H__3___ molecules of H22OO

Let’s Step It Up a LittleLet’s Step It Up a Little 2NH2NH44NONO33 + 3H + 3H22SS

_____ atoms of Nitrogen_____ atoms of Nitrogen _____ atoms of Hydrogen_____ atoms of Hydrogen _____ atoms of Oxygen_____ atoms of Oxygen _____ atoms of Sulfur _____ atoms of Sulfur _____ molecule/moles of NH_____ molecule/moles of NH44NONO33

_____ molecule/moles of H_____ molecule/moles of H22SS

Let’s Step It Up a LittleLet’s Step It Up a Little 2NH2NH44NONO33 + 3H + 3H22SS

__4___ atoms of Nitrogen__4___ atoms of Nitrogen __14___ atoms of Hydrogen__14___ atoms of Hydrogen __6___ atoms of Oxygen__6___ atoms of Oxygen __3___ atoms of Sulfur __3___ atoms of Sulfur __2___ molecule/moles of NH__2___ molecule/moles of NH44NONO33

__3___ molecule/moles of H__3___ molecule/moles of H22SS

You Must Be Joking!You Must Be Joking! 2Na2Na22COCO33 + 3CO + 3CO22 + 4NaCl + Mg(NO + 4NaCl + Mg(NO33))22

_____ atoms of Sodium_____ atoms of Sodium _____ atoms of Carbon_____ atoms of Carbon _____ atoms of Oxygen_____ atoms of Oxygen _____ atoms of Chlorine _____ atoms of Chlorine _____ atoms of Nitrogen_____ atoms of Nitrogen _____ atoms of Magnesium_____ atoms of Magnesium _____molecules/moles of Na_____molecules/moles of Na22COCO33 _____ molecule/moles of CO_____ molecule/moles of CO22 _____ molecule/moles of NaCl_____ molecule/moles of NaCl _____ molecule/moles of Mg(NO_____ molecule/moles of Mg(NO33))22

You Must Be Joking!You Must Be Joking! 2Na2Na22COCO33 + 3CO + 3CO22 + 4NaCl + Mg(NO + 4NaCl + Mg(NO33))22

__8___ atoms of Sodium__8___ atoms of Sodium __5___ atoms of Carbon__5___ atoms of Carbon __18___ atoms of Oxygen__18___ atoms of Oxygen __4___ atoms of Chlorine __4___ atoms of Chlorine __2___ atoms of Nitrogen__2___ atoms of Nitrogen __1___ atom of Magnesium__1___ atom of Magnesium __2___molecules/moles of Na__2___molecules/moles of Na22COCO33 __3___ molecule/moles of CO__3___ molecule/moles of CO22 __4___ molecule/moles of NaCl__4___ molecule/moles of NaCl __1___ molecule/moles of Mg(NO__1___ molecule/moles of Mg(NO33))22

C + OC + O22 CO CO22 This equation is already balancedThis equation is already balanced What if it isn’t already?What if it isn’t already?

C + OO COO

C + OC + O22 CO CO We need one more oxygen in the products.We need one more oxygen in the products. Can’t change the formula, because it Can’t change the formula, because it

describes what is produced.describes what is produced. Remember, oxygen is a diatomic molecule.Remember, oxygen is a diatomic molecule.

C + O COO

The other Oxygen must be used to make The other Oxygen must be used to make another COanother CO

But where did the other C come from?But where did the other C come from?

C +O

C

OO

OC

Must have started with two CMust have started with two C 2 C + O2 C + O22 2 CO 2 CO

C+

O

COO

OC

C

Rules for balancingRules for balancing

Write the correct formulas for all the Write the correct formulas for all the reactants and productsreactants and products

Count the number of atoms of each Count the number of atoms of each type appearing on both sidestype appearing on both sides

Balance the elements (make them same Balance the elements (make them same amount on reactant and product sides) amount on reactant and product sides) one at a time by adding coefficients one at a time by adding coefficients (the numbers in front).(the numbers in front).

Check to make sure it is balanced.Check to make sure it is balanced.

Never!Never! Change a subscript to balance an Change a subscript to balance an

equation.equation. If you change the formula you are If you change the formula you are

describing a different reaction.describing a different reaction. HH22O is a different compound than HO is a different compound than H22OO22

NeverNever put a coefficient in the middle put a coefficient in the middle of a formulaof a formula 2 NaCl is okay, Na2Cl is not.2 NaCl is okay, Na2Cl is not.

ExampleExample

H2 + H2OO2

Make a table to keep track of where you are at

ExampleH2 + H2OO2

Need twice as much O in the product

R PHO

22

21

ExampleH2 + H2OO2

Changes the O

R PHO

22

21

2

ExampleH2 + H2OO2

Also changes the H

R PHO

22

21

2

2

ExampleH2 + H2OO2

Need twice as much H in the reactant

R PHO

22

21

2

24

ExampleH2 + H2OO2

Recount

R PHO

22

21

2

24

2

ExampleH2 + H2OO2

The equation is balanced, has the same number of each kind of atom on both sides

R PHO

22

21

2

24

2

4

ExampleH2 + H2OO2

This is the answer

R PHO

22

21

2

24

2

4

Not this

ExamplesExamples

CHCH44 + O + O22 CO CO22 + H + H22OO AgNOAgNO33 + Cu + Cu Cu(NO Cu(NO33))22 + Ag + Ag Mg + NMg + N22 Mg Mg33NN2 2

P + OP + O22 P P44OO1010

Na + HNa + H22O O H H22 + NaOH + NaOH

ExamplesExamples

CHCH44 + 2O + 2O22 CO CO22 + 2H + 2H22OO 2AgNO2AgNO33 + Cu + Cu Cu(NO Cu(NO33))22 + +

2Ag2Ag 3Mg + N3Mg + N22 Mg Mg33NN2 2

4P + 5O4P + 5O22 P P44OO1010

2Na + 2H2Na + 2H22O O H H22 + 2NaOH + 2NaOH