【正文】 Chapter 8 化學(xué)反應(yīng)速率 Chemical kiics 授課對(duì)象 :10級(jí)藥學(xué)本科 掌握內(nèi)容 ?有效碰撞、活化分子、活化能的概念及活化能與活化分子數(shù)對(duì)反應(yīng)速率的影響。 ?溫度、濃度、催化劑對(duì)化學(xué)反應(yīng)速率的影響及濃度影響的定量關(guān)系 — 質(zhì)量作用定律、化學(xué)反應(yīng)的溫度因子。 ?反應(yīng)級(jí)數(shù)與反應(yīng)分子數(shù)概念。一級(jí)反應(yīng)的化學(xué)反應(yīng)速率方程式的計(jì)算。 了解內(nèi)容 ?化學(xué)反應(yīng)速率的基本概念。 ?二級(jí)、零級(jí)反應(yīng)的特征 ?均相催化作用的特點(diǎn)。 難點(diǎn) ?活化能與活化分子數(shù)對(duì)反應(yīng)速率的影響 ?根據(jù)給出的實(shí)驗(yàn)條件寫出化學(xué)反應(yīng)速率方程式及進(jìn)行有關(guān)的計(jì)算。 ?一級(jí)反應(yīng)的有關(guān)計(jì)算。 Chemical kiics 化學(xué)動(dòng)力學(xué) ?The area of chemistry that is concerned with the speeds, or rates, at which reactions occur is called chemical kiics 第一節(jié) 化學(xué)反應(yīng)速率的表示方法 Reaction rate 化學(xué)反應(yīng)速率 Definition : The ratio of the amount of decreasing in reactant or the amount of increasing in product to a specific time interval. 一定時(shí)間內(nèi)反應(yīng)物濃度的減少量或生成物濃度的增加量與時(shí)間間隔的比值 Unit: molL1 s 1(min1,h1) p r o d u c tr e a c t a n t ccvvtt??? ? ???(1) Average rate 平均速率 The change in the concentration of reactant or product during a time interval. p r o d u c tr e a c t a n t ccvvtt??? ? ???C h a n g e in th e c o n c e n tr a tio n o f s p e c ie sC h a n g e in tim eV ? The change in the concentration of reactant or product at one specific instant time. 在反應(yīng)時(shí)間間隔無(wú)限小時(shí)，反應(yīng)物濃度或生成物濃度的變化與時(shí)間間隔的比值 r a c t a n t p r o d u c tp r o d u c tr e a c t a n t dcdcvvd t d t? ? ?(2) Instantaneous rate 瞬時(shí)速率 H 2 O 2 ( a q ) H 2 O ( l ) + 12 O 2 ( g )I 2 2 2 20( H O ) d ( H O )l imdtccvtt????? ? ??說(shuō)明 ?用 反應(yīng)物 表示速率變化時(shí)應(yīng)標(biāo)上 負(fù)號(hào) ,以保證速率為正值 ?當(dāng)反應(yīng)速率穩(wěn)定時(shí) ， 反應(yīng)式中用不同物質(zhì)表示的速率間比值等于反應(yīng)式中各物質(zhì)的系數(shù)比 VA:VB:VC:VD=a:b:c:d ?化學(xué)反應(yīng)速率值必須注明是以反應(yīng)體系中的哪種化學(xué)物質(zhì)表示而得 化學(xué)反應(yīng)速率的表述之二 反應(yīng)進(jìn)度 ξ： ,0BBBBBnnn???????化學(xué)反應(yīng)速率 p r o d u c tr e a c t a n t11 BBB B B Bdcdcd n d cdvV d t V d t d t d t d t?? ? ? ?? ? ? ? ?＝單位體積內(nèi)反應(yīng)進(jìn)度隨時(shí)間變化率 此時(shí)的 v代表整個(gè)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(wú)關(guān) ?例： N2 + 3H2 2NH3 322 d ( N H )d ( N ) d ( H )11d 3 d 2 dcccvt t t? ? ? ? ?aA + bB = cC + dD 1 ( A ) 1 ( B ) 1 ( C) 1 ( D )dc dc dc dcva dt b dt c dt d dt? ? ? ? ? ?第二節(jié) 反應(yīng)機(jī)理 Reaction processes occur in a single event or step are called elementary steps. 一步就能完成的化學(xué)反應(yīng) A B C reactant product react Elementary reaction 元反應(yīng) ： A overall reaction consists of a sequence of elementary 反應(yīng)組成的化學(xué)反應(yīng)叫做非元反應(yīng) A B Reactants Intermediate product react … End product Multistep mechanisms (posite reaction) 非元反應(yīng)（復(fù)合反應(yīng)） Molecularity of reaction 反應(yīng)分子數(shù) 1SO2Cl2 = SO2 + Cl2 The sum of the stoichiometric coefficient 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) 單分子反應(yīng) :If a single molecule is involved, the reaction is said to be unimolecular. H 3 C N C H 3 CCNH 3 C C Nmethyl isonitrile rearrange 1NO2+ 1CO = NO + CO2 2NO + 1H2 = N2O + H2O 2I + 1H2 = 2HI 三分子反應(yīng) :Elementary steps involving the simultaneous collision of three molecules are said to be termolecular reaction 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)） . 2N2O5(g)→ 4NO2 (g)+O2(g) (A) N2O5 → NO3 + NO2 (slow， rate limiting step，速率控制步驟） (B) NO3 → NO+O2 (quick) (C) NO+NO3→ 2NO2 (quick) (A)(B)(C)三步就是該的反應(yīng)機(jī)理 Reaction mechanism反應(yīng)機(jī)理 The process by which a reaction occurs is called reaction mechanism . It involve one or more intermediates化學(xué)反應(yīng)進(jìn)行的實(shí)際步驟。即實(shí)現(xiàn)化學(xué)反應(yīng)的各步元反應(yīng)組合的微觀過(guò)程 Rate limiting step or ratedetermining H2 (g) +I2 (g) =2HI(g) (A) I2 (g) = 2I (quick) (B) H2 (g)+2I (g) = 2HI (g) (slow) （ Rate limiting step/ ratedetermining step） The slowest step in mechanism. 在化學(xué)反應(yīng)的實(shí)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(gè)復(fù)雜反應(yīng)的速率大小，這一較慢的元反應(yīng)稱為 速率控制步驟 ，簡(jiǎn)稱 速控步驟 第三節(jié) 化學(xué)反應(yīng)速率理論簡(jiǎn)介 ?碰撞理論 ?活化過(guò)渡狀態(tài)理論 碰撞理論與活化能 理論碰撞認(rèn)為：化學(xué)反應(yīng)的發(fā)生是反應(yīng)物之間發(fā)生有效碰撞的結(jié)果 有效碰撞 ： 能發(fā)生化學(xué)反應(yīng)的碰撞 彈性碰撞 ： 不能發(fā)生化學(xué)反應(yīng)的碰撞 (a)彈性碰撞 (b)有效碰撞 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) 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 second For example The prerequisites of effective collision 有效碰撞條件 (1) The molecules of the reactant must have enough energy. to stretch, bend, and ultimately break bonds, leading to chemical reactions. (1)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(jià)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)鍵破裂，而形成新的化學(xué)鍵，即形成新的分子 The prerequisites of effective collision 有效碰撞條件 (2)The colliding molecules with high energy must have a favorable orientation. (2) 具有高能量的分子間碰撞要有合適方向 分子在碰撞時(shí)，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)，才能使分子或離子的反應(yīng)部位間舊鍵破裂，新鍵形成 CO + NO2 → CO2 + NO O C O O N O N O C O Example The orientation factor Collisions must occur not only with sufficient energy but also with suitable orientation to cause reaction. Conditions of effective collision Activated molecule and activation energy 活化分子與活化能 ?Activated molecule A molecule which has enough kiic energy to take part in a 發(fā)生化學(xué)反應(yīng)的反應(yīng)物分子 ?Activation energy ( Ea ) The minimum energy of the activated molecule or the minimum energy required to initiate a chemical 最低能量與反應(yīng)物分子的平均能量之差 Ea= E’ E平均 氣體分子能量分布曲線 E平均 E’ Ea 活化分子 動(dòng)能 ENN??The characteristic of activation energy (1) Ea must be positive Ea depends on the nature of the reactant and the route of the reaction. Ea is different in different reaction. Ea is different in different route of a reaction. (2) Ea independ on temperature and concentration. (3) Ea↓， the fraction of activated molecule↑, the reaction rate ↑. Relationship among activation energy , activated molecules and reaction rates Ea2 Ea1 Activated molecules Kiic energy ENN???In a given temperature ?Ea↑， activated molecules↓， V ↓ ?Ea↓， activated molecules↑， V ↑ Ea Ea In general (1) Ea40