The Driving Forces of CHEMICAL REACTIONS

Precipitation Reactions EXCHANGE: Precipitation Reactions REACTIONS

IONIC COMPOUNDS Compounds in Aqueous Solution Most redox reactions are in water — aqueous solutions - and involve ionic compounds K+(aq) + MnO4-(aq) KMnO4 in water To play the movies and simulations included, view the presentation in Slide Show Mode.

Insoluble products: Precipitation formation

Precipitation Reactions The “driving force”= solid. Pb(NO3)2(aq) + 2 KI(aq) g 2 KNO3(aq) + PbI2(s) Net ionic equation Pb2+(aq) + 2 I-(aq) g PbI2(s)

Water Solubility of Ionic Compounds If one ion from the “Soluble Compound” list is present, the compound is water soluble.

Aqueous Solutions Solutions that conduct electricity are called ELECTROLYTES Strong electrolytes dissociate completely (or nearly so) into ions.

Aqueous Solutions CH3CO2H(aq) ---> CH3CO2-(aq) + H+(aq) Acids that ionize only to a small extent are called weak electrolyte. CH3CO2H(aq) ---> CH3CO2-(aq) + H+(aq)

Aqueous Solutions Some compounds dissolve in water but do not conduct electricity. They are called nonelectrolytes. Examples include: sugar ethanol ethylene glycol

Net Ionic Equations Mg(s) + 2 HCl(aq) g H2(g) + MgCl2(aq) We really should write Mg(s) + 2 H+(aq) + 2 Cl-(aq) g H2(g) + Mg2+(aq) + 2 Cl-(aq) The two Cl- ions are SPECTATOR IONS — they do not participate. Could have used NO3-.

We leave the spectator ions out — Net Ionic Equations Mg(s) + 2 HCl(aq) --> H2(g) + MgCl2(aq) Mg(s) + 2 H+(aq) + 2 Cl-(aq) ---> H2(g) + Mg2+(aq) + 2 Cl-(aq) We leave the spectator ions out — Mg(s) + 2 H+(aq) ---> H2(g) + Mg2+(aq) to give the NET IONIC EQUATION

EXCHANGE Acid-Base Reactions REACTIONS

Acid-Base Reactions The “driving force” = water. Net ionic equation OH-(aq) + H+(aq) g H2O(l) This applies to ALL reactions of STRONG acids and bases.

Know the strong acids & bases!

ACIDS Some strong acids are HCl hydrochloric H2SO4 sulfuric An acid g H+ in water Some strong acids are HCl hydrochloric H2SO4 sulfuric HClO4 perchloric HNO3 nitric HNO3

BASES Base g OH- in water NaOH(aq) ---> Na+(aq) + OH-(aq) NaOH is a strong base

CaO(s) + H2O(liq) g Ca(OH)2(aq) Indicator shows solution is basic. BASES CaO(s) + H2O(liq) g Ca(OH)2(aq) Metal oxides are bases CaO in water. Indicator shows solution is basic.

ACIDS CO2(aq) + H2O(l) g H2CO3(aq) SO3(aq) + H2O(l) g H2SO4(aq) Nonmetal oxides can be acids CO2(aq) + H2O(l) g H2CO3(aq) SO3(aq) + H2O(l) g H2SO4(aq) and can come from burning coal and oil.

EXCHANGE Gas-Forming Reactions REACTIONS

Gas Forming Reactions

Electrochemical Reactions REDOX REACTIONS REACTIONS

Why Study Redox Reactions Batteries Corrosion Manufacturing metals Fuels

Examples of Redox Reactions Combustion Fuel + Oxygen Metal (Mg) + Oxygen

Examples of Redox Reactions Synthesis Metal + halogen 2 Al + 3 Br2 ---> 2AlBr3

REDOX REACTIONS Redox reactions are characterized by ELECTRON TRANSFER between an electron donor and electron acceptor.

Lose electrons: OXIDATION Gain electrons: REDUCTION LEO says GER Lose electrons: OXIDATION Gain electrons: REDUCTION

REDOX REACTIONS Single replacement Cu(s) + 2 Ag+ (aq) gCu2+ (aq) + 2 Ag(s) In all reactions; if something is oxidized then something needs to be reduced

Elemental Oxygen always REDUCED (GAIN) Combustion Fuel + Oxygen Metal (Mg) + Oxygen

Elemental Metals Always OXIDIZED (LOSE) Cu + HNO3 Cu = oxidized HNO3 = reduced Mg + HCl Mg = oxidized H+ = reduced

OXIDATION NUMBERS The electric charge an element APPEARS to have when electrons are counted by some arbitrary rules:

Recognizing a Redox Reaction OXIDATION NUMBERS = CHARGE 2 Al(s) + 3 Cu2+(aq) --> 2 Al3+(aq) + 3 Cu(s) Al(s) --> Al3+(aq) + 3 e- Therefore, Al is OXIDIZED Ox. no. of Al increases as e- are donated by the metal.

Recognizing a Redox Reaction OXIDATION NUMBERS = CHARGE 2 Al(s) + 3 Cu2+(aq) --> 2 Al3+(aq) + 3 Cu(s) Cu2+(aq) + 2 e- --> Cu(s) Therefore, Cu is REDUCED Ox. no. of Cu decreases as e- are accepted by the ion.

REDOX REACTIONS EXCHANGE: Precipitation Reactions EXCHANGE Gas-Forming Acid-Base Reactions REACTIONS REDOX REACTIONS