Writing And Balancing Equations

Chemistry

Dr. May

The Road To Writing Sentences

Know the alphabetKnow vowels and consonantsKnow how to spell wordsKnow the meaning of wordsKnow sentence structureKnow capitalization and punctuation

The Road To Writing Equations

Know the atomic symbolsKnow oxidation numbers of elementsKnow the charge on polyatomic ionsBe able to create the correct formulas Identify the reactants and productsBalance the equation

The Language of Equations

Ca(OH)2 + H2SO4 CaSO4 + 2 H2O

The equation above is like a sentence

The compounds Ca(OH)2, H2SO4, CaSO4, and H2O are like correctly spelled and chosen words

The elements Ca, O, H, and S are like the letters of the alphabet

Equations in English

Ca(OH)2 + H2SO4 CaSO4 + 2 H2O

One molecule of calcium hydroxide plus one molecule of sulfuric acid yields one molecule of calcium sulfate plus two molecules of water.

Equations

Zn + 2 HCl ZnCl2 + H2

On the left, Zn and HCl are reactants On the right, ZnCl2 and H2 are products The arrow () means “yields” The up arrow () indicated a gas product The 2 in front of HCl is a coefficient The small 2 to the right of H is a subscript

“Skeleton” Equation Identify the reaction

Zinc reacts with hydrochloric acid to give zinc chloride and hydrogen gas

Determine the correct formulas and write the “skeleton” (unbalanced) equation

Zn + HCl ZnCl2 + H2

Coefficients A coefficient placed before a formula

multiplies every atom in that formula by that number

2 H2SO4

2 H2SO4 means 2 molecules of sulfuric acid but also

4 H atoms, 2 S atoms, and 8 O atoms

Conservation Of MassA balanced equation contains the same

number of each kind of atom on each side of the equation

The balanced equation obeys the

Law of Conservation of Mass

Balance The Equation

Zn + HCl ZnCl2 + H2

Count atoms of each element on each side

Balance each element by placing whole numbers (coefficients) in front of each formula as needed

Zn + HCl ZnCl2 + H2 2

Write EquationCalcium hydroxide reacts with sulfuric

acid to give calcium sulfate and water

Calcium = Ca+2

Sulfate = SO42Hydrogen = H+1

Hydroxide = OH1

Ca(OH)2 + H2SO4 CaSO4 + H2O

Balance Equation

1Ca, 2OH, 2H, 1SO4 1Ca, 1OH, 1H, 1SO4

Ca(OH)2 + H2SO4 CaSO4 + HOH

Count atoms on both sides

Balance the water

Ca(OH)2 + H2SO4 CaSO4 + HOH2

Write EquationAluminum hydroxide plus sulfuric acid

gives aluminum sulfate plus water

Aluminum = Al+3 Hydroxide = OH1

Hydrogen = H+1 Sulfate = SO42

Al(OH)3 + H2SO4 Al2(SO4)3 + H2O

Balance The Equation

Al(OH)3 + H2SO4 Al2(SO4)3 + HOH

1 Al, 3 OH, 2 H, 1 SO4 2 Al, 3 SO4, 1 H, 1 OH

2 Al(OH)3 + H2SO4 Al2(SO4)3 + HOH

2 Al(OH)3 + 3 H2SO4 Al2(SO4)3 + HOH

2 Al(OH)3 + 2 H2SO4 Al2(SO4)3 + 6 HOH

Write The EquationPropane burns to produce carbon

dioxide and water

C3H8 + O2 CO2 + H2O

The above skeleton equation must be balanced

Balance The EquationC3H8 + O2 CO2 + H2O

First balance the carbons

C3H8 + O2 3 CO2 + H2O

Next balance the hydrogens

C3H8 + O2 3 CO2 + 4 H2O

Finally balance the oxygens

C3H8 + 5 O2 3 CO2 + 4 H2O

6 + 4 = 10

2 x 5 = 10

Chemical Equations Chemical equations are the short hand

description of a chemical reaction

It tells us:

The reactants and products The formulas of the reactants and products The number of molecules of reactants and products The number of atoms of each element The number of moles of each substance

The EndThis presentation was created for the

benefit of our students by the Science Department at Howard High School of Technology

Please send suggestions and comments to rmay@nccvt.k12.de.us