CHEM 112 FINAL EXAM SG 1 EXAM 1 CONTENT REACTION RATES Concentration 2 molecules colliding Incr conc incr collision Incr rate of rxn Factors Physical State Temperature Molecules mix collision Molecules collide w KE Same state mixes better If dif larger SA makes more collisions incr rate of rxn Incr temp incr KE Incr rate of rxn Rate change of conc change in time So for A B A t B note A is neg bc transferring to B Rate Stoich For aA bB cC dD 1 A 1 B 1 C 1 D neg bc decr a t b t c t d t ex 2A 3B 1 A 1 B A 2 B t 3 t 2 t 3 t Rate Law For aA bB cC dD Rate k A m B n K rate constant m n rxn orders products are irrelevant CHEM 112 FINAL EXAM SG 2 Rxn Orders show how rate is affected by conc When m 1 if A doubles rate will double m 2 if A doubles rate with quadruple m 0 no change Units for orders 1 m s km m sm 2 m s km2 m sm 3 m s km3 m sm 1 s s 1 2 1 sm s 1m 1 2 s 1m 2 3 1 sm Integrated Rate law time dependent A B 1st order ln A ln A 0 kt ln A A 0 kt 2nd order 1 A t 1 A 0 kt Half life t1 2 1st order t1 2 693 k Other ln N t N 0 693t t1 2 Ea Temp is key Incr temp incr Ea incr freq of collision If final energy prod reactants Hrxn 0 If final energy prod reactants Hrxn 0 CHEM 112 FINAL EXAM SG 3 Temp w rate Arrhenius Equation ln k1 Ea 1 1 k2 R T2 T1 Slope Ea lnk2 lnk1 k k m in y mx b R 1 T2 1 T1 Mechanisms Unimolecular Bimolecular Termolecular A B C A B C D 2A C D A B C D E r k A r k A B r k A 2 r k A B C Overall rxn slowest rate Rate determining step Intermediate Product then reactants CHEM 112 FINAL EXAM SG 4 Catalyst Reactants then products Incr rate of rxn Lowers activation energy Never in rate law Doesn t increase yield Doesn t change H rxn Ex A B 2C 2D 2D C 2E B D intermediate B catalyst NUCLEAR Isotopes unstable bc not found in nature n p usually stable stability greatest for even weakest for odd Belt of Stability CHEM 112 FINAL EXAM SG 5 Beta Decay n p electrons lost atomic incr by 1 above belt proton deficient Positron Emission P n below belt Neutron deficient Positron Is lost Atomic decr by 1 Electron Capture P n opp of beta decay Electron gained Atomic decr by 1 CHEM 112 FINAL EXAM SG 6 Alpha Decay Emits a 4 2He atom Mass decr by 4 Atomic decr by 2 2 neutrons lost Disintegration Series Multiple decays Forms fission products Rate of Decay activity ALWAYS CONSTANT Rate kn always in first order ln Nt N0 kt Decay indep of conc Not dependent on temp press collisions or Ea Carbon Dating k decay constant n decaying atoms units of Bq Nuclear Half life t1 2 693 k CHEM 112 FINAL EXAM SG 7 Nuclear Binding Energy m mass of prod mass of reactants E m c2 E energy in J m mass in kg c speed of light Larger binding energy more stable Binding energy per nucleon E nucleons protons neutrons iron has most stable nucleus 2 light elements can join to get larger mass Fusion more stable exothermic Heavy elements break in two fission Exothermic bc more stable Uranium 235U 239U 233U 238U does not Nucleus Below small subcritical escape not causing fission 3 Med chain rxn constant rate above large supercritical few neutrons escape nuclear bomb Nuclear Reactors Medium mass percent of uranium Too small to be supercritical Give off heat to convert water to steam Cadium Boron rods absorb neutrons But build up so much fission need replaced Fuel Waste HAZARDOUS CHEM 112 FINAL EXAM SG 8 Key notes to remember Incr conc incr collision incr temp Incr conc incr rate Incr temp incr KE H Ea fwd Earev K Slope Ea R Rate independ on conc CHEM 112 FINAL EXAM SG 9 ACID BASE Acid EXAM 2 CONTENT Has H in water yields H3O Strength is based on amount of H3O Produced per mole of acid in water Strong Acid Dissociates completely in water equil H3O HA initial HA H A Ka will be high since H3O will be high Hydrohalic acids start w Cl go down group Oxoacids where there are 2 O than there are H HFO HFO2 HFO3 HFO4 Weak Acid Dissociates slowly in water equil H3O HA initial HA H A K or Ka Ka will be low since H3O will be low Base Acids where H is not bonded to an O HCN HF Oxoacids less than 2 more O than H HNO2 HClO Organics R COOH Substance that has OH in formula wields OH Strong Base M2O MOH where M represents any group 1 metal M OH 2 MO where M represents Ca Sr or Ba Weak Base Any compound where N has a lone pair is weak NH3 AUTOIONIZATION OF WATER Even pure water dissociates to form H3O OH ions H2O l H2O l H3O aq OH aq Kw H3O OH 1 00 x 10 14 250C concentrations of H3O OH are equal in pure water Acid H3O OH Base H3O OH both ions are always present Always true H3O x OH Kw pH SCALE CHEM 112 FINAL EXAM SG 10 Acidity Bases pH log H3O ex H3O 1x10 5 M has pH of 5 pOH log OH Also used to define equil constants K pK log K PKw pH pOH 14 298K 250C Acidity incr Ka incr pKa decr BRONSTED LOWRY Substances can yield OH even if they don t contain OH Acids proton DONOR Any species that donates H ions Acid must contain H in its formula Bases proton ACCEPTOR Any species that accepts H ions Base must contain lone electron pair that can bind to H some may act as either depending on mixture Amphoteric CONJUGATE ACID BASE PAIRS Can reverse Base Acid conj Base conj acid NH3 H2S HS NH4 Conj Base Conj Acid From acid that already donated proton Has 1 less H than acid Has 1 more negative charge From base that already fonated proton Has 1 more H than base 1 less negative charge RELATIVE STRENGTHS The stronger the acid the weaker the conj base Conj acid opp strength of conj base In contrast very weak acid will have very strong conj base Ex HClO4 is very strong acid ClO4 is a very weak base WEAK ACID EQUILIBRIUM Finding H3O by using ICE table CHEM 112 FINAL EXAM SG 11 Assume the following Initial acid conc is very large H3O from acid is very large compared to H3O from autoionization Polyprotic acids release …