Unit 4: Molecules and Bonding The Mechanics of Chemical Reactions

Unit 4: Goals Define Chemical Reaction Define Chemical Reaction List signs of a chemical reaction List signs of a chemical reaction Calculate oxidation numbers Calculate oxidation numbers Name compounds Name compounds Balance Chemical equations Balance Chemical equations Identify unknown substances based on their chemical properties Identify unknown substances based on their chemical properties

Unit 4: Key vocabulary Compound Compound A pure substance made of more than 1 elementA pure substance made of more than 1 element Molecule Molecule Two or more atoms combined, the simplest unit of a compoundTwo or more atoms combined, the simplest unit of a compound Chemical Reaction Chemical Reaction A change that takes place due to the combination, separation, or rearrangement of atomsA change that takes place due to the combination, separation, or rearrangement of atoms Oxidation Number Oxidation Number The charge of an ionThe charge of an ion

Signs of a chemical reaction Gas is produced Gas is produced Bubbles, air pockets, etc.Bubbles, air pockets, etc. Color change Color change The substance changes colorThe substance changes color Temperature change Temperature change Gets hot or cold quicklyGets hot or cold quickly Energy released Energy released Heat or lightHeat or light Precipitate forms Precipitate forms A solid forms from the combination of non- solid substancesA solid forms from the combination of non- solid substances

Types of Chemical Reactions

Exothermic Releases energy Releases energy Heat packHeat pack Ice meltIce melt

Endothermic Energy is absorbed Energy is absorbed Ice packIce pack Heat only travels one way Heat only travels one way

Synthesis Two or more substances combine to form a new compound Two or more substances combine to form a new compound A + X  AX A + X  AX 2Mg + O 2  2MgO 2Mg + O 2  2MgO

Decomposition A single compound undergoes a reaction that produces two or more simpler substances. A single compound undergoes a reaction that produces two or more simpler substances. Generally take place only when energy is added.Generally take place only when energy is added. AX  A + X AX  A + X 2H 2 O  2H 2 + O 2 2H 2 O  2H 2 + O 2

Single Replacement One element replaces a similar element in a compound. One element replaces a similar element in a compound. Must take place in an aqueous solutionMust take place in an aqueous solution A + BX  AX + B A + BX  AX + B Cl 2 + 2KBr  Cl 2 + 2KBr  2KCl + Br 2 2KCl + Br 2

Double Replacement Ions of two compounds exchange places in an aqueous solution to form two new compounds Ions of two compounds exchange places in an aqueous solution to form two new compounds AX + BY  AY + BX AX + BY  AY + BX HCl + NaOH  NaCl + H 2 O HCl + NaOH  NaCl + H 2 O