Equations & Equations & BalancingBalancing

OutlineOutline

Word EquationsWord Equations Skeleton EquationsSkeleton Equations Conservation of MassConservation of Mass Balanced Chemical EquationsBalanced Chemical Equations

Chemical EquationsChemical Equations Represent a Represent a chemical reactionchemical reaction..

Are made up of Are made up of twotwo parts: parts:

ReactantsReactants ProductsProducts

eg. methane + oxygen eg. methane + oxygen carbon dioxide + carbon dioxide + waterwater

CHCH44 + O + O22 CO CO22 + H + H22OO

Chemical EquationsChemical Equations

ReactantsReactants are listed on the are listed on the left sideleft side and and separatedseparated by a by a plus sign (+).plus sign (+).

ProductsProducts are listed on the are listed on the right sideright side and and separatedseparated by a by a plus sign (+).plus sign (+).

Word EquationsWord Equations

Word EquationsWord Equations – only the chemical – only the chemical names of the reactants and products names of the reactants and products are shown.are shown.

eg. eg. methane + oxygen methane + oxygen carbon dioxide + carbon dioxide + waterwater

Skeletal EquationsSkeletal Equations

Unbalanced system where the Unbalanced system where the chemical names are converted to chemical names are converted to chemical symbols/formulas.chemical symbols/formulas.

Eg.Eg. CHCH44 + O + O22 CO CO22 + H + H2200

Conservation of MassConservation of Mass

MassMass of the of the reactantsreactants = the = the massmass of of the the productsproducts..

Why?Why? AtomsAtoms are not are not created or destroyedcreated or destroyed

in a chemical change.in a chemical change.

FormulasFormulas for molecules for molecules cannotcannot be be changed.changed.

Balanced Chemical EquationBalanced Chemical Equation

When the When the reactantsreactants and and products products contain contain equal numbersequal numbers of the of the same atom the chemical equation same atom the chemical equation is is balancedbalanced..

Balanced by the use of coefficientsBalanced by the use of coefficients

Balanced Chemical EquationBalanced Chemical Equation

CoefficientsCoefficients are numbers written are numbers written in in frontfront of chemical formulas. of chemical formulas.

They They indicate numberindicate number of atoms or of atoms or molecules of that molecules of that substance.substance.

CHCH44 + + 22OO22 CO CO22 + + 22HH2200

CoefficientCoefficient

Balanced Chemical EquationBalanced Chemical Equation

Physical state symbols are added Physical state symbols are added to show the substance’s to show the substance’s compositioncomposition

((s) – solids) – solid (l) – liquid (l) – liquid (aq) – aqueous(aq) – aqueous (g) - gas(g) - gas

CHCH4(g)4(g) + + 22OO2(g)2(g) CO CO2(g)2(g)+ + 22HH220 0 (l)(l)

Balancing EquationsBalancing Equations

CHCH44 + O + O22 CO CO22 + H+ H2200

Type of atom Type of atom (symbol)(symbol)

# in reactants# in reactants # in products# in products

CC 1 1 1 1

HH 44 22

00 22 33

Balancing EquationsBalancing Equations

CHCH44 + O + O22 CO CO22 ++ 22HH2200

Type of atomType of atom

(symbol)(symbol)# in reactants# in reactants # in products# in products

CC 1 1 1 1

HH 44 44

00 22 44

Balancing EquationsBalancing Equations

CHCH44 + + 22OO22 CO CO22 ++ 22HH2200

Type of atomType of atom

(symbol)(symbol)# in reactants# in reactants # in products# in products

CC 1 1 1 1

HH 44 44

00 44 44

Balanced Chemical EquationBalanced Chemical Equation

General RulesGeneral Rules1)1) Balance metals Balance metals firstfirst..2)2) Balance Balance non-metalsnon-metals next (except next (except

hydrogen and oxygen). Polyatomic hydrogen and oxygen). Polyatomic ions can be balanced as a group.ions can be balanced as a group.

3)3) Balance Balance hydrogenhydrogen and and oxygenoxygen last. last.4)4) Ensure that the eqn is in lowest terms.Ensure that the eqn is in lowest terms.5)5) Check to ensure that there are the Check to ensure that there are the

same # of each type of atom before same # of each type of atom before and after the rxnand after the rxn

Balanced Chemical EquationBalanced Chemical Equation

Use Use coefficients coefficients to change the to change the numbernumber of atoms of an element. of atoms of an element.

NeverNever change the change the subscriptssubscripts..

Some equations may take longer Some equations may take longer than others to solve (than others to solve (be patientbe patient).).