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