www.hechemisryguru.com Re Lw Expression Order of Recion The order of recion is defined s he number of oms or molecules whose concenrion chnge during he chemicl recion. Or The ol number of molecules or oms whose concenrion deermine he re of recion is known s order of recion. Order of recion = Sum of exponens of he concenrion erms in re lw xa yb Producs By he re lw, Re x y [A] [B[, hen he overll order of recion. n x y, where x nd y re he orders wih respec o individul recns. If recion is in he form of recion mechnism hen he order is deermined by he slowes sep of mechnism. A 3B AB3 A B AB(fs) AB B AB 3(slow) (Re deermining sep) AB3 A AB 3(fs) (Here, he overll order of recion is equl o wo.) An order of recion my be zero, negive, posiive or in frcion nd greer hn hree. Infinie nd imginry vlues re no possible.
www.hechemisryguru.com Re Lw Expression () Firs order recion : When he re of recion depends only on he one oncenrion erm of recn. Exmples : A produc HO HO O All rdiocive recions re firs order recion. Re of growh of populion if here is no chnge in he birh re or deh re. Re of growh of bceril culure unil he nuriens re exhused. Excepion : HO, H, OH nd excess quniies re no considered in he deermining process of order. Exmples : CH3COOCH5 HO CH3COOH CH5OH; Order = ; r k [CH3COOCH 5] A(excess) B produc ; Order = ; R k [B] NO5 4NO O ; Order = ; R k [NO 5] ClO7 Cl 7O ; Order = ; R k [ClO 7]
www.hechemisryguru.com Re Lw Expression (i) recion 3 3 3 3 (CH ) C Cl OH (CH ) C OH Cl ; Order = ; R k [(CH 3) 3C Cl] Velociy consn for firs order recion : Le us ke he A Produc Iniilly = Afer ime = ( x) x Here, '' be he concenrion of A he sring nd ( x) is he concenrion of A fer ime i.e., x pr hs been chnged in o producs. So, he re of recion fer ime is equl o ( x) d or k( x) d or ( x) k.d..(i) inegred re consn is, k.33 log ( x)..(ii).33 log k ( x)..(iii) (ii) Hlf life period of he firs order recion : when / ; x, hen eq. (ii) becomes /.33 log k.33 k / ; / log
www.hechemisryguru.com Re Lw Expression.33.33 / log ( log.3 ); /.3 k k /.693 k Hlf life period for firs order recion is independen from he concenrion of recn..33 Time for compleion of n h frcion, / n log K n (iii) Uni of re consn of firs order recion : k (sec) () Second order recion : Recion whose re is deermined by chnge of wo concenrion erms is sid o be second order recion. For exmple, 3 5 3 5 CH COOH C H OH CH COOC H H O S O I SO I 8 4 (i) Clculion of re consn : A produc or A B produc When concenrion of A nd B re sme. A B Produc Iniilly Afer ime = ( x) (-x) x d k[a] [B] k [ x] [ x]
www.hechemisryguru.com Re Lw Expression k [ x] d ; Inegred equion is x k. ( x) ; x. k ( x) When concenrion of A nd B re ken differen A + B Produc Iniilly = b Afer ime = ( x) (b x) x d k [ x].[b x], Inegred equion is, k.33 b( x) log ; ( b) (b x).33 b( x) log k( b) (b x) (ii) Hlf life period of he second order recion : When / ; x ; / k ( ) k Hlf life of second order recion depends upon he concenrion of he recns. / (iii) Uni of re consn : k mol li sec n Δ n ; n, k mol li.sec (Where n order of recion)
www.hechemisryguru.com Re Lw Expression (3) Third order recion : A recion is sid o be of hird order if is re is deermined by he vriion of hree concenrion erms. When he concenrion of ll he hree recns is sme or hree molecules of he sme recn re involved, he re expression is given s 3A producs or A B C producs (i) Clculion of re consn : x( x) k. ( x) d 3 k( x), Inegred equion is (ii) Hlf life period of he hird order recion : Hlf life period = 3 k ; / ; Thus, hlf life is inversely proporionl o he squre of iniil concenrion. (iii) Uni of re consn : k mol ime or lire k lire mol ime (4) Zero order recion : Recion whose re is no ffeced by concenrion or in which he concenrion of recn do no chnge wih ime re sid o be of zero order recion. For exmple, Sunligh H Cl HCl Dissociion of HI on gold surfce. Recion beween ceone nd bromine. The formion of gs he surfce of ungsen due o dsorpion.
www.hechemisryguru.com Re Lw Expression (i) Clculion of Re Consn : Le us ke he recion A Produc Iniilly k[a] d, k d Inegred re equion, ; k. d he concenrion of he recing subsnce. x k ; The re of recion is independen of (ii) Hlf life period of zero order recion : When / ; / x ; or / ; The hlf life period is direcly proporionl o he k iniil concenrion of he recns. (iii) Uni of Re consn : mole k ; Uni of re of recion = li. sec. Uni of re consn. Noe : In generl, he unis of re consn for he recion of n h order re: Re k[a] n mol L s n k(mol L ) or k (mol L ) s n Unis of re consns for gseous recions: In cse of gseous recions, he concenrions re expressed in erms of pressure in he unis of mosphere. Therefore, he re hs he unis of m per second.
www.hechemisryguru.com Re Lw Expression Thus, he uni of differen re consns would be: (i) Zero order recion : (ii) Firs order recion : m s s (iii) Second order recion: m s (iv)third order recion: m s In generl, for he gseous recion of n h order, he unis of re consn re (m) n s Modified expressions for re consns of some common recions of firs order Recion N O NO O 5 k Expression for re consn.33 V log V V Here V volume of O fer ime nd V volume of O fer infinie ime. NH4NO (q) HO N Sme s bove, here V nd V re volumes of N ime nd infinie ime respecively..33 V HO HO O k log V Here V nd V re he volumes of KMnO 4 soluion used for irion of sme volume of recion mixure zero ime (iniilly) nd fer ime.
www.hechemisryguru.com CH COOC H 3 5 3 5 H H O CH COOH C H OH.33 V V k log V V Re Lw Expression Here V,V nd V re he volumes of NOH soluion used for irion of sme volume of recion mixure fer ime,, nd infinie ime respecively. C H O dsucrose H H O k.33 r r log r r C H O C H O 6 6 6 6 dglucose lfrucose (Afer he recion is complee he equimolr mixure of glucose nd frucose obined is levoroory) Here, r, r nd r re he polrimeric redings fer ime, nd infiniy respecively. Exmples of recions hving differen orders Exmples Re Lw Order Firs order recion HO HO O r k [H O ] CH5Cl CH4 HCl r k [CH5Cl] NO5 4NO O r k [N O 5] SOCl SO Cl r k [SO Cl ]
www.hechemisryguru.com Re Lw Expression CH3COOCH5 HO CH COOH C H OH 3 5 r k [eser][h O] CHO HO C H O C H O 6 6 6 6 r k [sugr][h O] All rdiocive decy r k [rdiocive species] Second order recions NO O NO O r k [NO] [O 3] 3 NO NO O r k [NO ] H I HI r k[h ][I ] CH3COOCH5 CH COO 3 5 OH C H OH r k [CH3 COC H 5] [OH ] C H H C H r k [C H ][H ] 4 6 4 NO N O CH3CHO CH4 CO r k [N O] r k [CH3CHO] Third order recions NO O NO r k [NO] [O ] 3 NO Br NOBr r k [NO] [Br ] 3 NO Cl NOCl r k [NO] [Cl ] 3 Fe I FeI r k [Fe ][I ] 3
www.hechemisryguru.com Re Lw Expression Zero order recions H Cl HCl (over wer) r k [H ] [Cl ] NH N 3H P 3 r k [NH ] 3 Frcionl order recions Pr H orho H r k [pr H ].5.5 CO Cl COCl r k [CO] [Cl ].5 / COCl CO Cl CH3CHO CH4 CO r k [COCl ] r 3/.5 3/ k [CH3CHO].5 Negive order recion O 3O 3 r k[o ] [O ] wih 3 respec o O. Overll order =