【物理化学Ⅱ】(10)- 化学动力学.ppt
物理化学物理化学()PHYSICAL CHEMISTRY (10)(10)8.11 Photochemical reaction-Photochemistry1.Introduction只有在光的作用下才能进行的反应称为光化学反应，简称光化反应。光合作用：胶片的感光：臭氧层的破坏：光化学烟雾Differences of Thermal reaction and Photochemical reaction:光化反应的G可能大于零。光化反应的活化能来源于光能（Chemistry of excited state)2.Excited states of molecules in photochemical reaction(1)Singlet state and Triplet statehh S0S 1T1S0S2S1T1S0磷光荧光Jablonski 图内转变系间窜越A+hA*A*A+S+heat 溶剂猝灭2A+heat 自身猝灭 A+M+heat 杂质猝灭P 反应A+h 辐射跃迁+S+A+M3.Principles of Photochemistry(1)The first law of photochemistry(grotthus-Draper)Only the light absorbed by the reactants is effective in producing a photochemical reaction(2)The second law of photochemistry(Stark-Einstein)In the primary step of a photochemical reactionone molecule is activated by one absorbed quantumof light(photon)if the strength of light is not very largeEnergy of photon1 mol光子的能量称为1 Einstein:frequency of photon:wave length of photon c:rate of light 各种光的 Einstein值:Light /m 1 Einstein/J mol-1ultraviolet 15040010-9 38105(紫外光)visual 40080010-9 1.5 3 105(可见光)infrared 800 10-9 310-5 150 4103(红外光)通常,电子的能级间隔 4105 J mol-1,所以,一般只有紫外光和可见光对光化反应起作用.A+h A*A*A+hAPCl2+h 2ClCl+H2 +HCl+H Quantum yield(量子产率量子产率)r:rate of photochemical reactionIa:Strength of light(单位时间单位体积吸收的光子的摩尔数)(3)Beer-Lambert LawIt:透射光强度I0:入射光强度:吸光系数c :溶质浓度d:溶液厚度 4.Rate equation of photochemical reaction5.Characteristics of photochemical reaction(1)G 可能大于零 (2)温度对光化反应速率的影响较小(3)photochemical equilibrium2C14H10 C28H20h,k+Q,k-At equilibrium(a)K和ce都与光强和光的波长有关(b)Gm-RTlnK(c)k+/k-Kc6.Photosensitization and sensitizer有些物质不能直接吸收某种波长的光进行化学反应,但如在反应体系中加入某种物质,则该物质能吸收此光能并将其传递给反应物,使之反应,而本身在反应前后并不发生变化,该物质称为光光敏剂敏剂,此类反应称为光敏反应光敏反应H2h(253.7nm)Hg(g)2H7.Laser chemistry特点:(1)高强度（I 可达到 1011W.cm-2)(2)单色性好（线宽可小于10-3 nm)(3)发散度小（聚焦后光斑面积可小于10-4cm）(4)脉冲宽度短（可达10-15 s）(5)偏振性好 应用：(1)激光分离同位素原子蒸汽多光子电离法分离铀同位素235U600nm235U+光化学的其它新进展:光电信息功能材料,光疗,(4)快速反应动力学 (3)微区激光化学(光刻)(2)激光诱导化学反应(选键化学)8.12 Measument of fast reaction 1.Relaxation method(M.Eigen,1954)快速反应测定的困难之一：无法准确确定反应的起始时间（反应与混合同时开始）解决的方法：在一定的条件下，使反应进行，直到平衡。突然改变反应条件，使平衡发生移动，直 至新的平衡，测定从旧的平衡至新的平衡 的时间（迟豫时间），从而计算出反应速 率。x0 xctTtt0tT1T2A +B C +Dk2k-2t=0 a a 0 0t=t a-x a-x x xIn equilibrium at T1In equilibrium at T2Set x=x-xe x=xe+xx xSet x0/x=e is called relaxation time测定和该反应的平衡常数，即可计算 k2,k-2。2、闪光分解（、闪光分解（flash photolysis)石英反应器电源CCA闪光灯F检测器Norrish-Porter(1948)(1967年获诺贝尔奖）H2O OH+HhOH+H2 H2O+HH+O2+M HO2+MHO2+HO2 H2O2+O2k4t/sLg(I0/I)k4=6109 dm3mol-1s-1205nm吸收光谱测定HO2的衰减曲线闪光光解法测定闪光光解法测定HO2自由基的动力学自由基的动力学8.13 Catalytic reaction Kinetics1.Catalysis and catalyst A catalyst is a substance that accelerate the reaction without undergoing a permanent chemicalchange itself in the process.催化作用的重要性2.Mechanism of catalysisA+B P加入催化剂CA+C AC k1k-1k2AC+B PA+B(AB)PE+C(AC)AC+B(ACB)+C催化剂通过参加反应,改变反应途径,降低活化能,而加快反应速率.2H2O2 2H2O+O2加入KIH2O2+I-IO-+H2OH2O2+IO-H2O+O2E=75 kJ mol-1E=59 kJ mol-13H2+N2 2NH3N2+2Fe 2N-FeH2+2Fe 2H-Fe N-Fe+H-Fe Fe2NH Fe2NH+H-FeFe3NH2 Fe3NH2+H-FeFe4NH3 Fe4NH34Fe+NH3(Adsorption)一些催化反应和非催化反应的活化能反反 应应 E/kJ mol-1 催化剂催化剂 非催化反应非催化反应 催化反应催化反应2HIH2+I2 184.1 104.6 Au2H2O 2H2+O2 244.8 136.0 Pt2N2O 2N2+O2 245 121 Au 134 Pt3H2+N2 2NH3 334.7 167.4 Fe-Al2O3-K2O2NH3 3H2+N2 335 163 W3.Basic characteristics of catalysis(1)The physical properties of catalyst can be changed after reaction.(2)A catalyst influences the rate of a chemical reaction but has no effect on the position of equilibrium.Ostwald experimentA(g)+B(g)=C(g)PCatalyst A catalyst accelerate the forward and reverse reactionsin the same propotion CO(g)+2H2(g)CH3OH(g)高压低压(3)Selectivity of catalystC2H2+O2CH2-CH2 OCH3CHOCO2+H2OK(250oC)1.61066.3 10184.0 10130(Ag)(Pd)(4)Effect of impuritiesAssisted catalyst:本身没有催化活性(或催化活性很小),但加入到催化剂中后会大大提高催化剂的活性的物质。如：合成氨Fe催化剂中加入的Al2O3和K2O。Poison:加入少量就能使催化剂的活性大大降低甚至消失的物质。暂时性中毒永久性中毒4.Classification of catalysisHomogeneous Gas catalysisLiquid catalysisAcid-base catalysisCoordination catalysisHeterogeneous catalysis Enzyme catalysis 5.Homogeneous catalysis(1)Acid-base catalysis C2H4+H2O C2H5OHH2SO4CH2 CH2+H2O C2H4(OH)2H2SO4OCH2 CH CH2+2H2O C3H5(OH)3+HClNaOHO ClMechanism:CH3OH+CH3COOHCH3COOCH3+H2OCH3OH+H+CH4OH+CH4OH+CH3COOH CH3COOCH3+H2O+H+S P酸催化S+H+SH+P+H+碱催化S+OH-SOH-P+OH-S:substrate(底物)Kw:ionic product of water酸碱催化反应的速率与溶液的pH值有关lnkpH7广义酸催化S+HA SH+A-P+HA广义碱催化 S+B S-+HB+P+B固体酸催化剂(环境友好催化剂)新型分子筛催化剂、大孔硅铝磷酸盐沸石催化剂、负载型磺酸盐/SiO2催化剂复习：12.13,12.9,12.10,12.11阅读:26.6作业：53,54 Physical Chemistry Exercises 26.6(b)
