Calculating Chemical EquationsCalculating Chemical Equations

Why and How Many Atoms Bond

Chemical EquationsChemical Equations

• A shorthand way to describe a chemical reaction using chemical symbols and formulæ

Chemical EquationsChemical Equations

• Has three parts• Reactants

• Substances present before the reaction

• Products• Substances present after the reaction

• Yield Arrow• Indicates the direction of a reaction• Some reactions are reversible

Writing a Chemical EquationWriting a Chemical Equation

Chemical symbols give a “before-and-after” picture of a chemical reaction

Reactants Products

MgO + C CO + Mg

magnesium oxide to form carbon monoxide

reacts with carbon and magnesium

Balancing Chemical Balancing Chemical EquationsEquations

• Equations must be balanced to observe the Law of Conservation of Matter• Matter can not be created or destroyed

under normal reactions• If you begin a reaction with 5 g of

Hydrogen, you must end up with 5 g of Hydrogen

A Balanced Chemical EquationA Balanced Chemical Equation

Same numbers of each type of atom on each side of the equation

Al + S Al2S3 Not

Balanced

2Al + 3S Al2S3 Balanced

Balancing Chemical Balancing Chemical EquationsEquations

• Count atoms on both sides of the yield arrow

• Determine which elements are unequal• Use coefficients to balance the number

of atoms on both sides• If you multiply one element in a compound,

you multiply both elements in a compound• You can treat Polyatomic Ions as one if

they appear on both sides of the equation• Go for the highest unequal elements first• Leave solitary elements for last

Steps in Balancing An EquationSteps in Balancing An Equation

Fe3O4 + H2 Fe + H2O

Fe: Fe3O4 + H2 3 Fe + H2O

O: Fe3O4 + H2 3 Fe + 4 H2O

H: Fe3O4 + 4 H2 3 Fe + 4 H2O

Balancing Chemical Balancing Chemical EquationsEquations

Mg + N2 Mg3N2

Al + Cl2 AlCl3

Balancing Chemical Balancing Chemical EquationsEquations

Fe2O3 + C Fe + CO2

Al + FeO Fe + Al2O3

Al + H2SO4 Al2(SO4)3 + H2

Types of Chemical ReactionsTypes of Chemical Reactions

• Synthesis• Two or more substances form one new

substance

H2 + O2 H2O

N2 + H2 NH3

Types of Chemical ReactionsTypes of Chemical Reactions

• Decomposition• One substance breaks down to form two or

more new substances

PbCO3 PbO + CO2

H2CO3 H2O + CO2

Types of Chemical ReactionsTypes of Chemical Reactions

• Single Displacement• One substance replaces another in a

compound

Li + AlCl3 LiCl + Al

Types of Chemical ReactionsTypes of Chemical Reactions

• Double Displacement• Two substances “swap partners” in two

compounds

KOH + HBr KBr + H2O

NaOH + H2CO3 Na2CO3 + H2O

Types of Chemical ReactionsTypes of Chemical Reactions

• Neutralization• Double-displacement reaction where an

acid and a base form a salt and water

KOH + HBr KBr + H2O

NaOH + H2CO3 Na2CO3 + H2O

Acids and BasesAcids and Bases• Acids

• Taste Sour• Have a pH of less than 7• Produce Hydronium H3O+1 in solution• Have an “extra” H- on the beginning of the

formula

H2SO4 – (Hydro)Sulfuric Acid

H3PO4 – (Hydro)Phosphoric Acid

HNO3 – (Hydro)Nitric AcidHCl – Hydrochloric Acid

Acids and BasesAcids and Bases• Bases

• Taste bitter• Have a pH of more than 7• Produce Hydroxide OH–1 in solution• Have an –OH on the end of the formula

NaOH – Sodium Hydroxide

KOH – Potassium Hydroxide

Ca(OH)2 – Calcium Hydroxide

NH4OH – Ammonium Hydroxide

The Litmus TestThe Litmus Test

• Using an indicator can tell whether a substance is acidic or alkaline

• Litmus paper is a frequently-used indicator• Acids turn BLUE litmus paper RED• Bases turn RED litmus paper BLUE

Types of Chemical ReactionsTypes of Chemical Reactions

• Combustion• Where a carbon compound combusts with

oxygen gas to form carbon dioxide and water

CH4 + O2 CO2 + H2O

C2H6 + O2 CO2 + H2O

Let’s get it startedLet’s get it started

• Some reactions require a little “jump start” to proceed

• Activation Energy• Energy required to be applied to start a

reaction

• Examples• Applying friction to start a match• The match causing a log to burn

Change in ENERGYChange in ENERGY• Every reaction has some change in

energy

• Two possibilities:

• Endothermic – absorbs energy from the environment to complete reaction• Feels “COLD” to its surroundings• Products have MORE energy than the

reactants

• Exothermic – releases energy to the environment as the reaction proceeds• Feels “HOT” to its surroundings• Products have LESS energy than reactants

Speeding Up

• A Catalyst is a chemical that participates in a chemical reaction without being changed by the reaction

• Catalysts speed up reaction rates by• acting as a “convenience”• lowering the activation energy

• Organic catalysts are called ENZYMES

Hungry?

• Without enzymes, your cells would NEVER keep up with the energy demands

Slowing Down

• An Inhibitor also participates in a chemical reaction without being changed by the reaction

• Inhibitors slow down reaction rates by• acting as an “inconvenience”• raising the activation energy

Normal reaction / normal activation energy

With a catalyst / lower activation energy

• Counting Atoms• Subscripts• Coefficients• Diatomic Molecules• Polyatomic Ions• Parenthesis• Oxidation Numbers• Binary Formulæ

• Criss-cross method

• Naming Rules• Ionic

• Roman Numerals

• Covalent• Prefixes

• Balancing Equations• NEVER change

subscripts• Law of Conservation

of Matter

• Types of Reactions• Changes in Energy

during reactions