Unit 4: Molecules and Unit 4: Molecules and BondingBonding

The Mechanics of Chemical The Mechanics of Chemical ReactionsReactions

Unit 4: GoalsUnit 4: Goals

Define Chemical ReactionDefine Chemical Reaction List signs of a chemical reactionList signs of a chemical reaction Calculate oxidation numbersCalculate oxidation numbers Name compoundsName compounds Balance Chemical equationsBalance Chemical equations Identify unknown substances based Identify unknown substances based

on their chemical propertieson their chemical properties

Unit 4: Key vocabularyUnit 4: Key vocabulary

CompoundCompound• A pure substance made of more than 1 A pure substance made of more than 1

elementelement MoleculeMolecule

• Two or more atoms combined, the simplest Two or more atoms combined, the simplest unit of a compoundunit of a compound

Chemical ReactionChemical Reaction• A change that takes place due to the A change that takes place due to the

combination, separation, or rearrangement of combination, separation, or rearrangement of atomsatoms

Oxidation NumberOxidation Number• The charge of an ionThe charge of an ion

Signs of a chemical reactionSigns of a chemical reaction

Gas is producedGas is produced• Bubbles, air pockets, etc.Bubbles, air pockets, etc.

Color changeColor change• The substance changes colorThe substance changes color

Temperature changeTemperature change• Gets hot or cold quicklyGets hot or cold quickly

Energy releasedEnergy released• Heat or lightHeat or light

Precipitate formsPrecipitate forms• A solid forms from the combination of non-solid A solid forms from the combination of non-solid

substancessubstances

Types of Chemical Types of Chemical ReactionsReactions

ExothermicExothermic

Releases energy Releases energy • Heat packHeat pack• Ice meltIce melt

EndothermicEndothermic

Energy is absorbedEnergy is absorbed• Ice packIce pack

Heat only travels one wayHeat only travels one way

SynthesisSynthesis

Two or more substances combine to Two or more substances combine to form a new compoundform a new compound

A + X A + X AX AX 2Mg + O2Mg + O22 2MgO 2MgO

DecompositionDecomposition A single compound undergoes a A single compound undergoes a

reaction that produces two or more reaction that produces two or more simpler substances. simpler substances. • Generally take place only when energy Generally take place only when energy

is added. is added.

AX AX A + X A + X 2H2H22O O 2H 2H22 + O + O22

Single ReplacementSingle Replacement One element replaces a similar element One element replaces a similar element

in a compound.in a compound.• Must take place in an aqueous solutionMust take place in an aqueous solution

A + BX A + BX AX + B AX + B ClCl22+ 2KBr + 2KBr

2KCl + Br2KCl + Br22

Double Replacement Double Replacement Ions of two compounds exchange Ions of two compounds exchange

places in an aqueous solution to form places in an aqueous solution to form two new compoundstwo new compounds

AX + BY AX + BY AY + BX AY + BX HCl + NaOH HCl + NaOH NaCl + H NaCl + H22OO