songhui化學(xué)反應(yīng)速率

1、1會計學(xué)songhui化學(xué)反應(yīng)速率化學(xué)反應(yīng)速率productreactant ccvvtt The change in the concentration of reactant or product during a time ductreactant ccvvtt Change in the concentration of speciesChange in timeV The change in the concentration of reactant or product at one specific instant time. 在反應(yīng)時在反應(yīng)時間間隔無限小

2、時，反應(yīng)物濃度或生成物濃度的間間隔無限小時，反應(yīng)物濃度或生成物濃度的變化與時間間隔的比值變化與時間間隔的比值ractantproductproductreactant dcdcvvdtdtH2O2(aq)H2O(l) +12O2(g)I-22220(H O )d (H O )limdtccvtt ,0BBBBBnnnproductreactant11BBBBBBdcdcdndcdvV dtVdtdtdtdt 單位體積內(nèi)反應(yīng)進(jìn)度隨時間變化率單位體積內(nèi)反應(yīng)進(jìn)度隨時間變化率此時的此時的v v代表整個化學(xué)反應(yīng)的速率，與反應(yīng)體系代表整個化學(xué)反應(yīng)的速率，與反應(yīng)體系中選擇何種物質(zhì)表示反應(yīng)速率無關(guān)中選擇何種物

3、質(zhì)表示反應(yīng)速率無關(guān)例： N2 + 3H2 2NH3322d (NH )d (N )d (H )11d3d2dcccvttt aA + bB = cC + dD1(A)1(B)1(C)1(D)dcdcdcdcvadtbdtcdtddt ABCreactantproductreactElementary reaction ：ABReactantsIntermediate productreactEnd productMultistep mechanisms (composite reaction)非元反應(yīng)（復(fù)合反應(yīng)）非元反應(yīng)（復(fù)合反應(yīng)）The sum of the stoichiometric c

4、oefficient of the reactants in elementary reaction.元反應(yīng)中反應(yīng)物系數(shù)之和稱反應(yīng)分子數(shù)元反應(yīng)中反應(yīng)物系數(shù)之和稱反應(yīng)分子數(shù)單分子反應(yīng)單分子反應(yīng):If a single molecule is involved, the reaction is said to be unimolecular.H3CNCH3CCNH3CCNmethyl isonitrile rearrange1NO2+ 1CO = NO + CO22NO + 1H2 = N2O + H2O 2I + 1H2 = 2HI三分子反應(yīng)三分子反應(yīng): :Elementary steps in

5、volving the simultaneous collision of three molecules are said to be termolecular reaction雙分子反應(yīng)雙分子反應(yīng): :Elementary steps involving the collision of two reactant molecules are said to be bimolecular reaction（注意：反應(yīng)分子數(shù)僅適用于元反應(yīng)）（注意：反應(yīng)分子數(shù)僅適用于元反應(yīng)）The process by which a reaction occurs is called reaction mec

6、hanism . It involve one or more intermediates化學(xué)反應(yīng)進(jìn)行的實際步驟。即實化學(xué)反應(yīng)進(jìn)行的實際步驟。即實現(xiàn)化學(xué)反應(yīng)的各步元反應(yīng)組合的微觀過程現(xiàn)化學(xué)反應(yīng)的各步元反應(yīng)組合的微觀過程The slowest step in mechanism.在化學(xué)反應(yīng)的實際步驟中，由許多元反應(yīng)組成在化學(xué)反應(yīng)的實際步驟中，由許多元反應(yīng)組成，其中最慢的那步元反應(yīng)限制著整個復(fù)雜反應(yīng)，其中最慢的那步元反應(yīng)限制著整個復(fù)雜反應(yīng)的速率大小，這一較慢的元反應(yīng)稱為的速率大小，這一較慢的元反應(yīng)稱為速率控制速率控制步驟步驟，簡稱，簡稱速控步驟速控步驟(a)彈性碰撞彈性碰撞 (b)有效碰撞有效碰撞

7、 反應(yīng)物分子互相接近，發(fā)生碰撞，碰撞后發(fā)生反應(yīng)物分子互相接近，發(fā)生碰撞，碰撞后發(fā)生化學(xué)反應(yīng)化學(xué)反應(yīng)僅有分子間的能量交換，不發(fā)生化學(xué)反應(yīng)僅有分子間的能量交換，不發(fā)生化學(xué)反應(yīng)H2 + I2 HI At room temperature the reaction proceeds very slowly . Only about 1 in every 1013 collisions produces a reaction effective collision . Each molecule undergoes about 1010 collisions per secondFor example

8、(1) The molecules of the reactant must have enough energy. to stretch, bend, and ultimately break bonds, leading to chemical reactions.(1)(1)反應(yīng)物分子要有足夠高的能量反應(yīng)物分子要有足夠高的能量以克服分子或離子外層價電子云間的排斥力以克服分子或離子外層價電子云間的排斥力而充分接近，產(chǎn)生電子重排，使舊的化學(xué)鍵而充分接近，產(chǎn)生電子重排，使舊的化學(xué)鍵破裂，而形成新的化學(xué)鍵，即形成新的分子破裂，而形成新的化學(xué)鍵，即形成新的分子(2) 具有高能量的分子間碰撞要有合適

9、方向具有高能量的分子間碰撞要有合適方向 分子在碰撞時，只有相互反應(yīng)的原子碰分子在碰撞時，只有相互反應(yīng)的原子碰撞在一起才可能發(fā)生化學(xué)反應(yīng)，才能使分子撞在一起才可能發(fā)生化學(xué)反應(yīng)，才能使分子或離子的反應(yīng)部位間舊鍵破裂，新鍵形成或離子的反應(yīng)部位間舊鍵破裂，新鍵形成OCOONO NO C OCollisions must occur not only with sufficient energy but also with suitable orientation to cause reaction.E平均平均EEa活化分子活化分子動能動能ENNEa2Ea1Activated moleculesKine

10、tic energyENNEaEaaERTfe有效碰撞頻率總碰撞頻率aERTvZ P fZ P eThe activated complex is not a stable molecule, and so it exists for only an instant before flying apart one way or the other. It flies apart because its potential energy is higher than that of either the reactant or the product molecules. Give out en

11、ergyAbsorbenergyA |AB |B+AABB2A-B orA-A+B-B分子變化分子變化能量變化能量變化Kinetic energyPotential energy反應(yīng)進(jìn)程反應(yīng)進(jìn)程ReactantActivated complex Productor reactantKinetic energyH反應(yīng)進(jìn)程的勢能圖反應(yīng)進(jìn)程的勢能圖A2+B2Reactants 2ABProductsEbEbComplex actived Potential energyE=H0 Exothermic reaction放熱反應(yīng)放熱反應(yīng)H3CCNH3CCNPotential energyH02CDRea

12、ction coordinatePotential energy(b)Figure5-7 Potential-energy changes during the course of a reaction: (a) Exothermic reaction. (b) Endothermic reaction.Ea EaEa 吸熱反應(yīng)吸熱反應(yīng)Ea The effect of the concentration on the reaction ratetan productreactCCvvtt NO2(g)+CO(g)NO(g)+CO2(g) When the temperature is fixe

13、d , the rate of a elementary reaction is proportional to the product of the molarity of the reactants , each raised to the power of its stoichiometric coefficient in the equation of the elementary reaction .2N2O5(g)4NO2(g)+O2(g) (3) The number of k amount to the number of rate when the concentration

14、 of every reactant is 1 molL-111ababABvvkvC C k is called specific rate(1)The rate law only can be applied to elementary reaction.只有元反應(yīng)，才可利用質(zhì)量作用定律直接寫出速只有元反應(yīng)，才可利用質(zhì)量作用定律直接寫出速率方程式率方程式(2)The rate equation of a non-elementary reaction depends on the results of experiment.對非元反應(yīng)，速率方程式由實驗測定對非元反應(yīng)，速率方程式由實驗測定N

15、2O5NO2O2(g)NO3NO2+(g)(g)N2O5(1)(2)(3)NO2+NO3+ NO2+ O2NO3+NONO2(overall reaction)(slow, rate-limiting step)(quick)(quick)52ONkcv Attention It is the sum of the exponents on the concentration terms in the rate equation.aA+bB=cC+dDyBxACkCv the order of reaction: n=(x+y)aA+bB=cC+dDIf it is a elementary

16、reaction:abABvkc cThe order of the reaction= a+b=molecularity of the reactionx=a；y=be.g：NO2+CO=CO2+NO (elementary reaction)2CONOvkccThe order of the reaction= 1+1=2=molecularity of the reactionReaction mechanism of CO+Cl2=COCl2 (phosgene)：(1)Cl22Cl（quick）212ClCl K 322Cl Cl ClK (2)Cl2+ Cl Cl3（quick）(

17、3)Cl3+COCOCl2+ Cl（slow，rate-limiting step）3ClCOvk cc322223ClCO32 ClClCO3232 Cl1 ClCOClCOvkcck K cc ck K cK cckcc32Cl2 ClClcK cc2Cl1 ClcK cThe overall reaction order is 1+3/2=2.5反應(yīng)級數(shù)反應(yīng)分子數(shù)使用范圍任何反應(yīng) 元反應(yīng) 取值 整數(shù)、分?jǐn)?shù)或負(fù)數(shù) 1，2，3與反應(yīng)物系數(shù)和的關(guān)系不一定相等相等 dcdcvkckdtdtc 00ln ktcktcc ec或0lglg2.303ktcc A first-order reactio

18、n is one whose rate depends on the concentration of a single reactant raised to the first power dcdcvkckdtdtc 000ln r lgc- lgc2.303ktcktocc ecktDefinite integralY = mx + blgct0The curve of first-order reactionslope-2.303k(1)012012ln 12ln20.693 cktctkk021C is one whose rate depends on the reactant co

19、ncentration raised to the second power or on the concentrations of two different reactants each raised to the first power.反應(yīng)速率與反應(yīng)濃度的二次方成正比反應(yīng)速率與反應(yīng)濃度的二次方成正比22 dcdcvkckdtdtc Definite integral011 ktccY = mx + b二級反應(yīng)方程式二級反應(yīng)方程式1/ct0Slope=k 01InterceptcThe curve of second-order reaction(1)1201tkc The rate o

20、f reaction is independent on the concentration of the reactant.0 dcvkckdt Definite integralc = - kt +coY = mx + b零級反應(yīng)方程零級反應(yīng)方程式式ct0(1)Slope= - kThe curve of zero-order reaction0122ctk反應(yīng)級數(shù)反應(yīng)級數(shù)一級反應(yīng)一級反應(yīng)二級反應(yīng)二級反應(yīng)零級反應(yīng)零級反應(yīng)方程式方程式lgc =-kt/2.303 +lgc0 1/c = kt +1/c0c = -kt + c0 直線關(guān)系直線關(guān)系lgct1/ctct斜率斜率-k/2.303k-

21、kk單位單位s-1Lmol-1s-1molL-1s-1t1/20.693/k1/k c0c0/2kOrder First-Second-Zero-Equationlgc =-kt/2.303 + lgc01/c=kt+1/c0c=-kt+c0 Straightlinelgct1/ctctSlope-k/2.303k-kk (unit)s-1Lmol-1s-1molL-1s-1t1/20.693/k1/k c0c0/2kThe rate equation of the reaction:2N2O5NO2+O2 is listed below,25 N Ovkcaccording to25 N O

22、vkcThe reaction is a first-order reaction:02lg-2.3030.51.68 1060lg- 0.182mol/L2.303 cktccc-102.50.5mol L5c N2O5 remainsn(N2O5)=cV=0.1825=0.91molThe consumption of N2O5n(N2O5)=2.5-0.91=1.59molThere is a reaction :HbO2HbO2+in the blood of lung, it is first-order in Hb (hemoglobin) and also first-order

23、 in O2, the normal concentration of Hb and O2 are 8.010-6 molL-1 and 1.610-6 molL-1 respectively.at 37，k=2.1106mol-1L-1s-1(1) please calculate how quickly the HbO2 was created in the blood of lung(2) if suffering some kind of disease, V(HbO2)=1.110-4 molL-1s-1 in order to keep cHb unchanged,how much

24、 the c(O2) is in oxygen therapy. Because it is first order in Hb and also in O2It is known that the k of a reaction is 1.2410-4s-1, please calculate its half life. No matter the reaction is endothermic or exothermic, its rate increase with increasing temperature.aERTkAek is the rate constantEa is th

25、e activation energy R is the gas constant 8.314J/mol-KT is the absolute temperature.A:Called the frequency factorlnlnaEkART lglg2.303EakART21211 2lnrmkHTTkRTTuT2 T1 時時 k2 k1 ，反應(yīng)速率，反應(yīng)速率lglg2.303EakARTu當(dāng)當(dāng)T一定一定 時時,lgA一定一定,則則Ea愈大愈大, k愈小愈小，v愈慢愈慢u對不同的反應(yīng)對不同的反應(yīng),溫度對反應(yīng)速率影響程度不溫度對反應(yīng)速率影響程度不同。當(dāng)同。當(dāng)T相同相同 時，時，Ea愈大，愈

26、大，斜率斜率Ea /T愈大愈大，k的的變化程度愈大變化程度愈大T/CT/Kk 10-51/T10-3lnk189.7462.92.522.160-10.589198.8418-9.855230.3503.56.301.986-7.370251.2507-5.757vant Hoff law：k (t+10)： rate constant at (t+10)kt： rate constant at t ：temperature coefficient.For a reaction , T, ； T , When the reactant is fixe

27、d, reaction rate increase 2 or 4 times with increasing temperature 10. 42k kt10t動能動能T T1 1T T2 2T T2 2 T T1 1()aNNEEaHigh temperatureLow temperatureMolecular kinetic energyFraction of molecules having a given kinetic energy Minimum energy needed for reaction,EaOrder First-Second-Zero-Equationlnc =-k

28、t + lnc01/c=kt+1/c0c=-kt+c0 Straightlinelnct1/ctctSlope-kk-kk (unit)s-1Lmol-1s-1molL-1s-1t1/20.693/k1/k c0c0/2kLower temperatureHigher temperatureKinetic energyMinimum energy needed for reaction,Ea EaEa加水溶解加水溶解NaCl物質(zhì)以分子或離子為物質(zhì)以分子或離子為單位互相混合，系統(tǒng)中單位互相混合，系統(tǒng)中沒有界面，這類系統(tǒng)稱沒有界面，這類系統(tǒng)稱為均相系統(tǒng)或均勻系統(tǒng)為均相系統(tǒng)或均勻系統(tǒng)如如NaCl溶液

29、溶液加水加水沙子沙子系統(tǒng)中有界面，界面兩側(cè)物質(zhì)具有不系統(tǒng)中有界面，界面兩側(cè)物質(zhì)具有不同的物理性質(zhì)和化學(xué)性質(zhì)同的物理性質(zhì)和化學(xué)性質(zhì)如泥漿、油水混合物等如泥漿、油水混合物等 A+C AC+B AB+C兩反應(yīng)途徑活化能：兩反應(yīng)途徑活化能：Ea1 Ea 、Ea2 Ea加入催化劑后，改變了化學(xué)反應(yīng)途徑，加入催化劑后，改變了化學(xué)反應(yīng)途徑，降低了活化能，反應(yīng)速率得以提高降低了活化能，反應(yīng)速率得以提高Ea2加入催化劑加入催化劑C后的反應(yīng)途徑后的反應(yīng)途徑：A + B ABEaEa1A + BABHEEE逆E逆途徑途徑1途徑途徑2BAcc 2kBACC 2kBAcc 2k2BckA + BABE2E1E1E2Ro

30、ute 1Route 2Ea1, Ea2 EaEa2In new route with catalyst C：A + B ABEaEa1 A+C AC+B AB+CThe activation energy of the reaction in new route is less than the activation energy of the reaction in original route, that increase the fraction of activated molecules in system, and increase the rate.（3）A catalyst

31、usually lowers the overall activation energy for a reaction by providing a completely different mechanism for the reactionH2O2(aq)2H2O+(l)Br-2(aq)+2H+Br2(aq)bromide ion2H2O2(aq)2H2O+ O2(l)(g)hydrogen peroxide+ O2(g)Br2(aq)+ H2O2(aq)Br-2(aq)+2H+bromineIn the absence of a catalyst this reaction occurs

32、 at an extremely slow rateA catalyst,bromide ion speeds the overall reaction without itself undergoing any net change.C2H4(g)+ H2(g)C2H6(g)ethyleneethaneThis reaction takes place very slowly under ordinary conditions. In the presence of a heavy metal such as nickel, palladium, or platinum, it occurs

33、 quickly at room temperature. The catalyzed reaction occurs at active sites on the surface of the solid. To maximize the surface area of the metal, it is used in the form of a fine powderlock-and-keyOdtdCvdtdCvCACA （2）the number of reaction rate of a reaction is connective with the change of the con

34、centration of the substance selected to express the reaction rate in a specific time interval. So we must give a clear indication of which substance was used to express the reaction rate.VA , VB , VC , VDtCtCCVIHHI2221加水溶解加水溶解NaCldissolvedNaClin water加水加水沙子沙子watersandHeterogeneous systemcollidingrea

35、ctionEffective collisioncollidingmove awayElastic collisionAABBAABBAABBReactants(initial state)Activated complex(transition state )Products(final state)Figure5-6 The activated complex物理論假設(shè)前題理論假設(shè)前題Hypothetical preconditions of the theoryCollision theory ：the molecule must have enough energy. The colliding molecules must have a favorable orientation. Transition state theory: (be similar with the above)The prerequisites of a reactionCollision theory ：the mol