המחלקה : ביולוגיה מולקולרית הפקולטה למדעי הטבע

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1 טל : פקס : ראש המחלקה: ד"ר אלברט פנחסוב המחלקה : ביולוגיה מולקולרית הפקולטה למדעי הטבע Course Name: Physical Chemisry - (for Molecular Biology sudens) כימיה פיזיקאלית )לסטודנטים לביולוגיה מולקולארית( Degree: B.Sc. / Course number: -750,/ Semeser B, nd annual hour Schedule: Wednesday, 3:00 5:00 Lecurer: Dr. Alex Lugovsoy Office locaion:..8 Tel lugovsa@ariel.ac.il Office hours: Sun. Mon. 9:30-:30 (phone appoinmen mandaory) Course goal: Broadening he nowledge of Physical Chemisry Course plan: Theme Lecure Exercise Par. Soluions Concenraion. Ways of expressing he concenraion Parial Molar Quaniies 3 Ideal Soluions 4 Dilued Soluions Par. Chemical Kineics 5 Kineics of Homogenous reacions. Reacion rae 6 Mass Acion Law 7 Moleculariy and Reacion Order 8 Temperaure dependence of he reacion rae 9 Acivaed Complex Theory 0 Kineics of Heerogeneous reacions Molecular diffusion

2 Fic's laws 3 Diffusion conrol and ineic conrol Par 3. Caalysis 4 Caalysis. Basics of he Caalysis heory Prerequisies: Physical Chemisry Mehod of insrucion: Fronal lecure + fronal exercises + homewor Course requiremens: Aendance and home exercise submission; exam Dae of he examinaion: As scheduled by he deparmen Course grading: Exam (80%), aendance and exercise submission (0%) Main exboo and addiional ex boos:. Ains P. W. Physical Chemisry, 4 h ediion, Oxford Universiy Press, Chang R. Physical Chemisry wih Applicaions o Biological Sysems, NY, 977. Required maerial for he examinaion: Lecures and exercises Sample examinaion: Choose one correc answer of four and answer of quesions. 8% each answer + 4% for he paricipaion. Sample Exam. The pre-exponenial facor for he molecular diffusion of ehanol in waer is D 0 = m / sec and he energy of acivaion of his diffusion process is E d =0J/mol. If a he emperaure of 90ºC he pressure is lowered so ha all he componens are gases (and hen D 0 = m /sec), he diffusion coefficien becomes: a. 0 7 imes larger

3 b. 0 7 imes smaller c. he same (does no change) d. senseless For he given diffusion processes in a liquid and in a gas he diffusion coefficiens are: D(l) = D o exp (-Ea/RT) = exp (-0000 / ) = m /sec D(g) = D o (T/98). = (363/98). = Their raio is: D(g)/D(l) 0 7 Therefore, he diffusion in he gas medium is by he facor of 07 faser han ha in he liquid. The answer (a) is rue.. Kineic conrol over a heerogeneous reacion is observed, when: a. he diffusion sage is significanly faser ha he chemical reacion b. here is no mass-ransfer a he r.d.s. c. he diffusion sage is significanly slower ha he chemical reacion d. he raes of mass-ransfer and of produc molecule formaion are approximaely equal. By definiion, ineic conrol is he case, when he acivaion sage (ha is, he chemical reacion) is he slowes. Therefore, answer (a) is rue for he simples mechanism. 3. A emperaure T 0 a heerogeneous reacion is conrolled by he diffusion. Provided is he acivaion sep rae and D is he (normalized) diffusion coefficien, he oal reacion can be represened by he following plo:

4 D D D T T T T T o T o T o T o a b с d Since he reacion a T 0 is conrolled by he diffusion, mus be higher han D. This is he case of plo (c). 4. I was found ha for he molar volume of an aqueous soluion of ammonia he * * following equaion hold rue: V 0.9( x V x V ), where x i is he molar NH 3 NH3 HO HO fracion of an i-h componen and V* i is he parial molar volume of ha componen. I can be concluded ha: a. ammonia reacs wih waer forming a basic soluion. b. he ineracion beween waer and ammonia is sronger han he ineracion beween waer and waer and beween ammonia and ammonia. c. he ineracion beween waer and ammonia is weaer han he ineracion beween waer and waer and beween ammonia and ammonia. d. ammonia displaces waer in he liquid phase * * From he equaion V 0.9( x V x V ) follows ha he molar volume of he NH 3 NH3 HO HO soluion is only 9% of wha i was supposed o be had he componens been mechanically (wihou any addiional ineracion) mixed. Tha is, he soluion is addiionally conraced on he mixing. And his evidences ha he ineracion beween waer and ammonia is sronger han he ineracion beween waer and waer and beween ammonia and ammonia (answer (b)).

5 5. Vapor pressure above pure hepane a some emperaure is 40 mmhg and ha above pure hexane a he same emperaure is 0 mmhg. The vapor pressure above a soluion conaining 0 mass% of hexane in hepane is: a. 4.5 mmhg b. 4.0 mmhg c mmhg d mmhg Because of he similariy of hexane and hepane he soluion can be considered ideal. Therefore, Raoule's law is applicable: p i = p i 0 x i The pressure above he soluion is he sum of each componen's pressures. We only miss he values of x i o calculae he vapour pressure above he soluion. Assume, we have 00 gr of he soluion: 0 gr hexane and 80 gr of hepane. The molar masses are: hexane C 6 H 4 84 gr/mol and hepane C 7 H 6 00 gr/mol. Find he numbers of moles of boh componens: n = m/m n(hexane) = 0 / 84 = 0.38 mol, n(hepane) = 80 / 00 = mol The oal number of moles is =.038 mol Hence, x(hexane) = 0.38 /.038 = 0.9 x(hepane) = 0.9 = 0.77 p (hexane) = 40 mmhg 0.9 = 3 mmhg p (hepane) = 0 mmhg 0.77 = 9.5 mmhg The vapour pressure above he soluion is ( ) = 4.5 mmhg. 6. For wo reacions he iniial concenraion of componen A was doubled. The halflife ime of he s reacion didn' change, while ha of he nd reacion lessened by he facor of wo. I can be concluded ha: a. reacion is s order, reacion is nd order b. reacion is nd order, reacion is s order

6 c. reacion is s order, reacion is 0 h order d. reacion is 0 h order, reacion is nd order The equaions of half-life imes are given on he Formulas Page (enclosed o your exam quesionnaire). These are: ( 0) / C0 ( ) / ln () (3) / C / 0 C0 3 I follows from he equaions ha only for he s order he half-ime does no depend on he concenraion. Therefore, reacion has he s order. The half-ime is inversely proporional o he concenraion only for he nd order. Therefore, reacion has he nd order. Answer (a) is rue. 7. Considering he following experimenal daa: Experimen # C A, mol / L C B, mol / L Rae, mmol / L s I can be concluded ha he ineic equaion of he reacion is: a. v = C A C B b. v = C A c. v = C B d. v = C AC B As seen from experimens # and #, he rae does no change a all when C A is doubled. Therefore he reacion order on A is 0. However, he doubling of C B (experimens #3 and #4) maes he rae by he facor of (9. /.3) = 4 faser. 4 =, herefore he reacion order on B is. Hence, v = C BC 0 A = C B (answer (c)).

7 8. As he emperaure rises from 5ºC o 35ºC, he reacion rae grows hree-fold. The energy of acivaion for his reacion is: a. 799 J/mol b. 9 J/mol c J/mol d. 8 J/mol Arrhenius' equaion reads: e Ea RT We will wan o find he rae consan raio for wo emperaures: e e e Ea RT Ea RT Ea R T T from he las line we can obain E a : ln ( / ) = - (E a /R)(/T /T ), Ea = Rln ( / ) (T T /(T T ) Ea = 8.34 ln3 (308 98/0) = J/mol (answer (c)). 9. I was found for a cerain reacion ha i proceeds faser as he emperaure rises, bu he use of a sirrer in a reacion vessel does no mae i go faser. I can be concluded ha: a. he reacion is conrolled by he diffusion b. he reacion is conrolled by he ineics c. he reacion has a mixed conrol ype d. he reacion is heerogeneous.

8 Temperaure affecs boh mass-ransfer and ineics. Bu sirring affecs only mass-ransfer. Therefore, he r.d.s is cerainly no diffusion. Therefore, answers (a) and (c) are wrong. As for answer (d), i is simply irrelevan. Hence, answer (b) is rue. 0. Which of he following plos characerizes a nd order reacion? C lnc /C /(C ) a b с d Kineic equaions for differen order reacions are given on he Formulas Page (enclosed o your exam quesionnaire). These are: C (0) C0 C 0 () ln () C C C C C 0 0 (3) For he nd order ineics he dependence of (/C) vs. is linear, which is he case in plo (c).. The unis of he rae consan for he 3 rd order are: a. mol L - sec - b. sec - c. mol - L sec - d. mol - L sec -

9 The simples form of a 3 rd order ineic equaion is: v = C 3 Hence = v C -3 Since [v] = mol L - s - and [C] = mol L -, [ III ] = (mol L - s - ) ( mol L - ) -3 = mol - L sec - (answer (d)).. (Mar all incorrec answers) The emperaure affecs: a. reacion order b. reacion rae c. rae consan d. moleculariy Reacion rae and moleculariy do no depend (a leas, in normal cases) on he emperaure. Answers (b) and (d) should be mared.