Week 7 of Dr. Ma's notes
Week 7 of Dr. Ma's notes CHEM 1200
Popular in Chemistry II
Popular in Chemistry
This 5 page Class Notes was uploaded by Alexi Martin on Thursday March 10, 2016. The Class Notes belongs to CHEM 1200 at Rensselaer Polytechnic Institute taught by Dr. Alexander Ma in Spring 2016. Since its upload, it has received 29 views. For similar materials see Chemistry II in Chemistry at Rensselaer Polytechnic Institute.
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Date Created: 03/10/16
Ch 15 Chemical Kinetics example 1: lnk2/2k1= Ea/R(1/300)(1/31) ln2 = Ea/8.31491.075x10^4 Ea= 5.35x10^4 J/mol Collision Theory of Kinetics in order for most reactions to take place, molecules must collide at 10^9 collisions/sec molecules collide if: 1 enough E to break bonds 2 colliding in the proper orientation to be effective they must be fast enough to overcome bonding forming, some effective, some are not Effective Collisions conditions net= effect greater the frequency the greater the reaction rate effective collision formation of the activated complex A is the frequency factor collision frequency z # collisions/sec more=effective k=A(e^ Ea/RT = pz(e^ Ea/RT) orientation factor p<1 most, more complex<p, atoms where p equals p spherical, p>1 e transfer old bonds break and new bonds can form Molecular interpretation reactant nature reactions occur faster in solutions mixing more particle contact, segregation more collisions, break bonds that need to be broken different rates and increase in potential energy closer to the activated complex and a reaction can lower the activation energy Temperature increase temperature increases kinetic energy min amount kinetic energy causes potential energy to form activated complex an increase in the number of molecules that can overcome activation complex Concentration/partial pressure except 0 order reactions more molecules=more collisions for effective collisions yield a biggers curve multimolecular collisions made up of several small reaction collisions 3 or fewer molecules Reaction Mechanism nist reactions occur in small reactions with 1,2 or 3 molecules series of reactions: reaction mechanism knowing rate law helps us understand the sequence in the mechanism example 2: H 2+2ICl>2HCl+I2 1 H2+ICl>HCl+HI 2HI+ICl>HCl+I2 produced and consumed=intermediates(HI) the overall rate law cannot have the concentrations of intermediates reactions are elementary they cannot be broken down into simpler steps, molecules interact directly without any other steps Molecularity # reactant particles in an elementary step unimolecular 1 bi 2 ter 3( rare) Rate laws for elementary reactions each step is its own reaction with its own rate law and Ea rate law overall is found experimentally can be deduced using equation of the slow or the rate law step rate determining steps one step occurs slower than others result formation of products cannot occur faster than the slowest which determines the overall reaction rate slowest step rate determining step increases Ea example 3: NO2+CO> NO+CO2 rate= k[NO2]2 NO2+NO>NO3+NO slow rate determining step NO3+CO>NO2+CO2 Validate 1. elementary steps yields an overall reaction 2. rate law predicted must be consistent with experimentally determined rate law Mechanisms with a fast initial step may contain intermediates substitute in rate law: left hand side must be just reactants example 3: NO>N2O2 H2+N2O2>H2O+N2O slow rate=k[H2][N2O2] H2+N2O>H2)+HN example4: O3> O2+O O3+O>2O2 rate f=rate r K[O3]=k[O2][O] [O]=[O3][O2]^1 rate=[O3]^2[O2]^1 example5: A+B2> AB+B slow rate determining step ate=k[A][B2] A+B>AB 2A+B2>2AB *Look at Clicker Problems* Catalysts affects rate by decreasing or increasing activation energy consumed in early mechanism and formed in a later step step up rate can be hetero different or homo same (phases) example 6: HQ2R2+ Ri> Q2R2 +HR Q2R2. Q2R+R rate determining slow step rate2=k2=[Q2R2]= k[HQ2R2][R]/[HR] r ate= k[HQ2R2][R]/[HR] Enzymes heterogenous biological reaction absorb substrate onto an active site products lock and key mechanism Chapter 17 Acids and Bases (II) arrhenius acid produce H+ ions arrhenius base produces OH ions when they react they create water and a salt HCl+NaOH>NaCl+H2O bronsted lowry acid H+ is transferred (proton) H donor bronsted Lowry base H acceptor an atom with an unshared pair of electrons HA+B:> :A+HB+ Lewis acid e pair acceptor Lewis base e pair donor Amphoteric substances : can be an acid or base such as water Strong or weak strong acid= strong electrolyte, all molecules ionize such as HCl strong base= strong electrolyte, all molecules ionize such as Ca(OH)2 strong base(#nOH)= OH ion ion concentration weak acid/base weak electrolyte only some of the molecule will ionize Strength of acid/base determined by finding equilibrium constant Ka or Kb farther towards products: stronger father towards reactants: weaker Ka size of equilibrium Ka=[acid][H3O+]/[HA] larger the Ka the stronger acid Ion product of H2O H3O+ and OH the same [H3O+][OH]=1.0x10^14 @ 25 degrees C called Kw, water dissociation constant one is given than the other can be calculated if [H3O+] is greater [OH] must be lower pH pH of water is 7(neutral) greater than 7 is basic, less than 7 is acidic pH= log[H3O]+ H3O+=10^pH pH+pOH=14 pK (unique to acid/ base strength) pKa= log(Ka) or 10^Ka=pKa pKb= log(Kb) or 10^Kb=pKb stronger acid smaller the pKa Kb=[OH][HB]/[B] stronger the base the smaller the pKb larger the Kb stronger base pH of a weak acid solve equilibrium H3O+ using I.C.E. chart Polyprotic Acids more than 1 H+ donor can have 1,2 or 3 ionizes in steps, each is removed sequentially each removal of H is harder AcidBase of salts salt water soluble ionic compounds cation strong base, weak acid anion are basic Na HCO3 cation weak base anion strong acid NH4Cl stronger the acid, weaker the conjugate base strong the base weaker the acid weaker the acid, stronger the conjuagate base weaker the base stronger the acid example 1: NO3 netural HCO3 basic Ka(Kb)=Kw Metal cations as weak acids cations increase charged metals Al3+ is acidic example 2: C5H5NH2+ acidic Ca2+ neutral Cr3+ acidic ● think about where they come from Acidity and Bascitiy of ions anion of a strong acid neutral HCl HBr= Cl Br So4 2 cations of strong bases are neutral Ca(OH)2 NaOH= Na+ K+ Mg+ Ca2+ anions of weak acids are basic HF= F CH3COO cations of weak bases are acidic NH3> NH4+ small increase charged metal cations are weak acids Al3+ Cr3+ Classify Salt salt cation is a counter ion of a strong base and anion of conjugate base of a strong acid= neutral NaCl Ca(NO3)2 KBr salt cation counter ion of a strong base and anion of a conjugate base of a weak acid = basic Ca(C2H3O2)2 KNO2 salt cation is a conjugate acid of a weak base and anion is a conjugate base of a strong acid= acidic NH4Cl salt cation increased charged metal ion, anion conjugate base of a strong acid acidic Al(NO3)3 salt cation of conjugate acid of weak base when conjugate base of weak acid, pH depends on strength of the acid or the base NH4F = acidic Ka>Kb acidic Kb>Ka basic example 3: S rCl2 neutral AlBr3 acidic CH3NH3NO3 acidic NaCHO2 basic NH4F acidic KNO3 neutral COCl3 acidic Ba(HCO3)2 basic CH3NH3NO3 acidic ionization of polyprotic acid Ka1>Ka2>Ka3 except H2SO4 example 4: 12 M H2CO2 Ka= 4.3x10^7 Ka2= 5.6x10^11 *Ka2 does not affect pH* H2CO3+H2O>HCO3+H3O+ HCO3+H2O>CO32+H3O+ I 0.12 +x +x x^2/0.12=4.3x10^7 x= log(2.27x10^4)=3.64 Cx H2SO4 strong acid completely dissociates use Ka2 example 5: HSO4 +H2O>SO42+H3O+ I 0.01 0.01 0.01 x(0.01+x)/0.01x use quadratic formula C x +x +x x= log(0.045)=.839 Binary acid strength increases across a period, HC<HN<HO<HF increase in bond energy the weaker the acid strength increases down a column HF<HCl<HBr<HI Oxyacids more electronegative Y atom stronger HClO>HIO more oxygens=stronger the acid acidity increases down the group acidity of oxyacids increases across a period HNO3>H2CO3>H3PO4>H3BO3 increase of oxidation # on central atom, stronger the oxy acid example 6: cidity (least to most) H3AsO3<H3PO3<H3PO4<HNO3 acidity (least to most) HS<H2S<HCl<HBr basicity (least to most) NO3<HCO3<CO32<BO33