山东大学：《物理化学》课程教学资源（讲义资料）9.2 Rate and rate equation-2 - for students

89.2 Reaction rate and rate equation I.R. Levine, pp 528-533 17.1 reaction kinetics 17.2 measurement of reaction rates

§9.2 Reaction rate and rate equation I. R. Levine, pp. 528-533 17.1 reaction kinetics; 17.2 measurement of reaction rates

89.2 Reaction rate and rate equation (1) Expression of reaction rate The rate (r of a chemical reaction is defined as the concentration change of a reactant or a product per unit time A mean rate △A]c2-C1 instantaneous rate: r △t Physical meaning Initial instantaneous rate?

The rate (r) of a chemical reaction is defined as the concentration change of a reactant or a product per unit time. (1) Expression of reaction rate instantaneous rate: d[A] r dt = t1 t c 2 1 2 1 [A] = c c r t t t  − =  − mean rate t c t1 t2 c1 c2 Physical meaning: Initial instantaneous rate? §9.2 Reaction rate and rate equation

89.2 Reaction rate and rate equation (1) Expression of reaction rate N,+3H,==2NH dc dt It is apparent that NH When expressed using different species, the rate of the reaction may attain different values, which is not convenient and sometimes may even cause confusion

N2 + 3H2 == 2NH3 2 2 H H dc r dt = − 2 2 N N dc r dt = − 3 3 NH NH dc r dt = It is apparent that N H NH 2 2 3 1 1 3 2 r r r = = When expressed using different species, the rate of the reaction may attain different values, which is not convenient and sometimes may even cause confusion. (1) Expression of reaction rate §9.2 Reaction rate and rate equation

89.2 Reaction rate and rate equation (1) Expression of reaction rate Definition Definition extent of reaction or advancement(5) The true rate of the reaction or rate of conversion ( dt where v is the stoichiometric coefficient of the reaction What is its Unit? +3H2==2NH3 aA+bB→gG+hH

Definition: extent of reaction or advancement () i i,0 i n n   − = where i is the stoichiometric coefficient of the reaction. Definition: The true rate of the reaction or rate of conversion (J): dt d J  = aA + bB → gG + hH What is its Unit? (1) Expression of reaction rate §9.2 Reaction rate and rate equation N2 + 3H2 == 2NH3

89.2 Reaction rate and rate equation (1) Expression of reaction rate When the reaction takes place in a container For general reaction: with constant volume or in solution without aA+bB→gG+hH change of solution volume When the extent ofreaction is ds Define rate dh l5 h d[a l d[a 1 dg] 1 d[hi J=2=- dna=- 1 dng- 1 dnu r= a dt b dt g dt h dt g I d cl n olm- s

For general reaction: aA + bB → gG + hH When the extent of reaction is d A B H G dn dn dn dn d a b g h  = − = − = = 1 1 1 1 A B H G d dn dn dn dn J dt a dt b dt g dt h dt  = = − = − = = When the reaction takes place in a container with constant volume or in solution without change of solution volume Define rate V J r = (1) Expression of reaction rate §9.2 Reaction rate and rate equation dt d dt h d dt g d dt b d a r 1 [A] 1 [A] 1 [G] 1 [H] = − = − = = dt d c r i i 1 [ ]  = Unit: mol m-3 s -1

89.2 Reaction rate and rate equation (2)Kinetic curve 1a[c;] Initial rate kinetic curve dc dt Rate at any time t=o t=t

(2) Kinetic curve i r  1 = dt d ci [ ] kinetic curve =0       = dt t dc r Initial rate dt t t dc r =       = Rate at any time t = 0 t = t t c §9.2 Reaction rate and rate equation

89.2 Reaction rate and rate equation (3)Concentration Measurements How can we determine the extent of the following reactions? CH3COOC2H5+NaOH→ N2O5=N2O4+0.5O2 CH3COONa+ C2HSOH Chemical method Physical methods

How can we determine the extent of the following reactions? CH3COOC2H5 + NaOH → CH3COONa + C2H5OH (3) Concentration Measurements §9.2 Reaction rate and rate equation N2O5 = N2O4 + 0.5 O2 Chemical method: Physical methods:

89.2 Reaction rate and rate equation (3)Concentration Measurements V. Ueber das Gesell. nach welchem die eingir C12H2O1+H2O—)C6H12O6+C6H12O6 kung der Sauren auf den Rohrzucker stattfindet son Ludwig Wilhelmy in Heidelberg sucrose glucose fructose Der die polarisationsebene des durch seine anfloenng ge henden Lichts nach rechtsdrchende rohrzucker wird b kanntlich durch Einwirkung von Sauren in linksdrchenden Substance sucrose glucose fructose Schleimzucker verwandelt. Da man nun mit Hilfe eines Polarisationsapparat, namentlich unter Anwendung der So. leil'schen Doppelplatte, nit grosser Leichtigkeit und Sicher aln25+665° +520 92 heit der Ablesung in jedem Augenblicke bestimmen kanD, wie weit diese Umwandlung vorgeschritten ist, so schien mir hierdnrch die Moglichkeit gegeben, die gesetze des in Rede stehenden Vorgangs zu ermitteln, andererseits aber die Aufgabe von Interesse, festzustellen, in welcher Weise die chemische Action, wenigstens in diesem speciellen Falle, der aber gewifs nur ein einzelner. Reprasentant einer gro fseren Reihe von Erscheinuugen seyn wird,-denn in der The first successful example for measuring Natur folgt Alles allgemeinen Geselzen abhangig sey von sammtlichen ihr Eintreten bedingenden Unstanden. Ich glaubte, dafs man auf diesem Wege werde feststel- concentration of reactant physically was len konnen, in welcher Weise diese Action- ahnlich wie der Dampfdruck und die Ausdehnung der Korper -eine Function der Temperatur sey, in wiefern sie - analog made by Wilhelmy in 1850 der elektrischen und magnetischen Anziehung und Absto [sung -ihrem Werth nach abhangig sey von dem Ab

The first successful example for measuring concentration of reactant physically was made by Wilhelmy in 1850 . §9.2 Reaction rate and rate equation (3) Concentration Measurements C12H22O11 + H2O ⎯→ C6H12O6 + C6H12O6 sucrose glucose fructose Substance sucrose glucose fructose []D 25 +66.5 o +52 o - 92 o

89.2 Reaction rate and rate equation (3)Concentration Measurements 表1蔗糖水解过程中的旋光度(=-43) t/ein a 1/min a visin a t/min a timin a I 31992166212.78570.0671-1 1.91245.8122.24 33178-19 3.0 995254178|821 2.0430456481.28609827 2.8 拟合直线:3.550.05104x 1733395081218243 2.6 187563633554042-1459257 2.4 氵22 三2 1.6 f/ min

§9.2 Reaction rate and rate equation (3) Concentration Measurements

89.2 Reaction rate and rate equation (3)Concentration Measurements FTIR spectroscopy Stretch of epoxy group 762 1745 910 8支 1600 1400 1200 100o

Stretch of epoxy group FTIR spectroscopy §9.2 Reaction rate and rate equation (3) Concentration Measurements