一級反應(yīng)動(dòng)力學(xué)、二級反應(yīng)動(dòng)力學(xué)基本原理

1、編輯pptKinetics動(dòng)力學(xué)Thermodynamics determines whether and in which direction a reaction will happen, and what the concentrations of constituents are involved in the reaction熱力學(xué)決定了反應(yīng)是否發(fā)生、反應(yīng)的方向以及參與到反應(yīng)之中的物質(zhì)濃度問題。Kinetics say how fast a reaction happens, sequence of steps in the reaction, and some of the fac

2、tors that control the rates of reactions動(dòng)力學(xué)則說明反應(yīng)發(fā)生的速率有多快、反應(yīng)步驟的順序以及控制反應(yīng)速率的一些因素Further Reading (Chapter 3 in Hobbs)編輯ppt Rate of reaction is typically measured as the change in concentration (moles/L) with time反應(yīng)速率通常通過濃度反應(yīng)速率通常通過濃度(mol/L)隨時(shí)間的變化來測量隨時(shí)間的變化來測量 This change may be a decrease or an increase改變

3、可能是增加的也可能是減小的改變可能是增加的也可能是減小的 Likewise the concentration change may be of reactants or products同樣，改變濃度的物質(zhì)可能是反應(yīng)物也可能是生成物同樣，改變濃度的物質(zhì)可能是反應(yīng)物也可能是生成物Rate = _ = _change in timechange in timein productsin reactantsRate =concentration changetime change反應(yīng)速率=濃度/時(shí)間編輯ppt Rate has units of moles per liter per unit t

4、ime- M s-1, M h-1速率的單位是摩爾每升每單位時(shí)間，如速率的單位是摩爾每升每單位時(shí)間，如M s-1、M h-1 Consider the hypothetical reaction 對于這個(gè)假設(shè)的反應(yīng)對于這個(gè)假設(shè)的反應(yīng)aA + bB cC + dD We can write t ARate of reaction=1a t B1b t C1c t D1d=-編輯ppt Note the use of the negative sign注意負(fù)號(hào)的使用注意負(fù)號(hào)的使用- rate is defined as a positive quantity反應(yīng)速率被定義為正量反應(yīng)速率被定義為正量

5、- rate of disappearance of a reactant is negative那么，反應(yīng)物的消耗速率就是負(fù)的那么，反應(yīng)物的消耗速率就是負(fù)的2N2O5(g) 4NO2(g) + O2(g) t N2O5Rate of reaction=12 t NO214 t O2=-編輯ppt Rate may be expressed in three main ways:反應(yīng)速率主要有以下三個(gè)表達(dá)方式：反應(yīng)速率主要有以下三個(gè)表達(dá)方式： Average reaction rate: a measure of the change in concentration with time 1、

6、平均反應(yīng)速率：濃度隨時(shí)間變化的度量、平均反應(yīng)速率：濃度隨時(shí)間變化的度量2. Instantaneous rate: rate of change of concentration at any particular instant during theReaction 2、瞬時(shí)速率：反應(yīng)過程中某一特定瞬間的濃度變化速率、瞬時(shí)速率：反應(yīng)過程中某一特定瞬間的濃度變化速率3. Initial rate: instantaneous rate at t = 0- that is, when the reactants are first mixed 3、初始速率：、初始速率：t=0時(shí)即反應(yīng)物最初混合時(shí)

7、的瞬時(shí)速率時(shí)即反應(yīng)物最初混合時(shí)的瞬時(shí)速率，編輯pptRate Laws 速率定律Rate law = a mathematical function describing the turnover rate of the compound of interest as a function of the concentrations of the various species participating in the reaction 速率定律：用來描述相關(guān)的化合物的轉(zhuǎn)化速率的數(shù)學(xué)函數(shù)，即各種參與反應(yīng)的物質(zhì)的濃度的函數(shù)May or may NOT have a theoretical bas

8、is可能有或沒有理論基礎(chǔ)“Many reactions occur at a decreasing rate with increasing time because the reaction rate diminishes as the concentrations of the reactants diminish”“很多反應(yīng)隨著時(shí)間的增加反應(yīng)速率逐漸減??？，因?yàn)榉磻?yīng)物濃度減小會(huì)降低反應(yīng)速率”Hobbs (2000)編輯pptRate Laws-dAdt=kAm“m” indicates the order of the reaction with respect to species “

9、A”. Determined experimentally.“m”指關(guān)于物質(zhì)A的反應(yīng)級數(shù)，由實(shí)驗(yàn)確定?！発” = rate coefficient (or specific reaction rate coeff.); determined for a specific reaction at a specific temp“K”=速率常數(shù)（或特定的速率系數(shù)），由特定溫度下的具體反應(yīng)確定A = productsReaction rate編輯pptRate LawsdAdt=-kAmBnCo“m, n, o” indicate the order of the reaction with res

10、pect to each species; determine experimentallyoverall reaction order = m+n+o“m, n, o”分別是關(guān)于每種物質(zhì)的反應(yīng)級數(shù)，實(shí)驗(yàn)確定的總反應(yīng)級數(shù)=m+n+oReaction orders can be: first, second, third反應(yīng)級數(shù)可以是一級、二級、三級A + B + C = products編輯pptFirst order reactions一級動(dòng)力反應(yīng)-dAdt=kA1=kAktteAA-=0Take integral of equation above, and get equation be

11、low:將以上等式積分，得到下面的等式：編輯pptt = 0.693 / kPlot of first order reaction一級動(dòng)力反應(yīng)的圖片半衰期的長度固定編輯pptExample of 1st order reaction1級動(dòng)力反應(yīng)范例If a reaction has a single reactant and the value of the exponent is one, then it is said to be a first-order reaction. 如果反應(yīng)物只有一種，而且指數(shù)為1，那么稱這種反應(yīng)為一級動(dòng)力反應(yīng)Write rate law for above

12、 equation:H2O2 (l) H2O(l) + 1/2O2(g)Wikipedia編輯pptSecond Order Reaction二級動(dòng)力反應(yīng) If integrated如果積分: 得到1/At = k”t + 1/Ao Inverse concentration linear in time 濃度的倒數(shù)和時(shí)間程線性關(guān)系-dAdt=kA2編輯pptt = 1 / k AoPlot of second order reaction 2級動(dòng)力反應(yīng)圖AtimeHalf lives are not constant with time for second order reactions二

13、級反應(yīng)動(dòng)力學(xué)反應(yīng)物質(zhì)的半衰期隨時(shí)間推移變化編輯pptExample of 2nd order reaction二級動(dòng)力反應(yīng)范例A second-order reaction depends on the concentrations of one second-order reactant, or two first-order reactants.二級動(dòng)力反應(yīng)取決是否有一個(gè)二級反應(yīng)物或者兩個(gè)一級反應(yīng)物？Write rate law for above equations:2NO2 (g) 2NO(g) + O2(g)WikipediaCO2 + H2O H2CO3編輯pptPseudo fi

14、rst order reactions偽一級反應(yīng) pseudo-first order: concentration of one reactant remains essentially constant over time (often because it is in large excess compared to the other reactant) 偽一級動(dòng)力反應(yīng)：一種反應(yīng)物剩余的濃度基本不變（經(jīng)常由于它與其他物質(zhì)相比，濃度過量）A+BC+DdAdt=-kABdAdt=-kA where k=kBlnA= lnA0-kt B濃度不變編輯pptReaction Mechanism反

15、應(yīng)機(jī)理 Often we write a chemical reaction 我們經(jīng)常寫化學(xué)反應(yīng)式 How we write it is often not how it happens 但是我們所寫的通常不是它如何發(fā)生的 Many kinds of reaction mechanisms 有很多反應(yīng)的機(jī)理編輯pptSingle Step (Elementary) Reaction Process單步（基本）反應(yīng)過程 Unimolecular 單分子反應(yīng) CaCO3 Ca2+ + CO32- Bimolecular 雙分子反應(yīng)CO2 + H2O H2CO3 Termolecular 三分子反應(yīng)

16、2 FeS2 + 3 O2 + 2 H2O 2 Fe3+ + 4H2SO4 No four or more molecule processes have been identified because chances of 4 molecules colliding is very, very small (making reaction rate super small)沒有4或者4以上的分子反應(yīng)被檢測到，因?yàn)?分子同時(shí)碰撞的機(jī)會(huì)非常非常?。ㄊ沟梅磻?yīng)速率非常?。┚庉媝ptRate Laws For Elementary基本反應(yīng)速率定律 Simple to write 書寫簡單 Unimol

17、ecular H2CO3 H+ + HCO3-dH2CO3/dt = kH2CO3 Bimolecular CO2 + H2O H2CO3dCO2/dt = kCO2H2O編輯pptReaction order is not necessarily related to the stoichiometry of the reaction, unless the reaction is elementary.反應(yīng)級數(shù)不一定和反應(yīng)的化學(xué)計(jì)量數(shù)有關(guān)，除非反應(yīng)是基本反應(yīng)In single step process, reaction order = coefficient of reactant in

18、 chemical equation在單步反應(yīng)過程中，反應(yīng)級數(shù)=化學(xué)式中反應(yīng)物的系數(shù)Complex reactions may or may not have reaction orders equal to their stoichiometric coefficients復(fù)雜反應(yīng)的反應(yīng)級數(shù)可能和化學(xué)計(jì)量系數(shù)相等Not all first order reactions, are single step, monomolecular reactions不是所有的一級反應(yīng)都是單步反應(yīng)、單分子反應(yīng)Important Note重要提示Hobbs (2000)編輯pptOverview of Ele

19、mentary Reactions基本反應(yīng)回顧Note: for Zero-Order reactions rate is independent of the concentration of reactant. Doubling concentration has no effect on rate.提示：零級反應(yīng)速率不依賴反應(yīng)物的濃度，雙倍的反應(yīng)物濃度不影響反應(yīng)速率。編輯pptArrhenius Equation and Transition State Theory阿倫紐斯方程和過渡態(tài)理論 reactions occur as a sequence of elementary step

20、s 化學(xué)反應(yīng)會(huì)發(fā)生一系列的基本步驟. usually one of these steps is much slower than the others Rate Determining Step 通常其中的一個(gè)步驟會(huì)比其他的步驟反應(yīng)慢很多，這個(gè)就是速率決定步驟 empirically, the effect of T on the rate of this reaction step (and therefore on the overall reaction rate) is described by the Arrhenius equation: 依照經(jīng)驗(yàn)，時(shí)間對這個(gè)步驟反應(yīng)速率（也就是

21、整體反應(yīng)速率）的影響可以用阿倫紐斯方程描述kA eERTa=-/pre-exponential factor or “frequency factor”A：指前因子或振動(dòng)因子describes collision frequency and the orientation probability描述碰撞頻率和定向概率Activation energy活化能（Ea是物質(zhì)分裂形成新物質(zhì)的最低能量） describes the fraction of species with energy greater than Ea 描述了物質(zhì)能量大于Ea的部分?編輯pptIncreased Temperatu

22、re = Faster Reaction Rates升溫=更高的反應(yīng)速率編輯pptDetermination of Activation Energy (Ea)活化能測定ln k2 - ln k1 = -Ea/R(1/T2 - 1/T1)K = reaction rate 反應(yīng)速率Ea = activation energy 活化能R = gas constant (8.314 J/mol*K, or 0.008314 KJ/mol*K) 氣體常數(shù)T = temperature in Kelvin 開爾文溫度編輯pptExample: 例如k is determined at two diff

23、erent temperatures for the following reaction: 在如下反應(yīng)中，兩種不同的溫度確定了兩個(gè)k值 2 HI(g) - H2(g) + I2(g)k1 = 2.15 x 10-8Ms-1 at 650Kk2 = 2.39 x 10-7Ms-1 at 700KDetermine the activation energy.編輯pptFig. 13.20a,b編輯ppt Three processes can explain slowness to reach equilibrium conditionsTransportDiffusionSurface Ch

24、emical Kinetics三個(gè)過程可以解釋達(dá)到反應(yīng)平衡緩慢的原因輸運(yùn)擴(kuò)散表面化學(xué)動(dòng)力學(xué) 編輯pptDrever (1997)Example of diffusion limitations 擴(kuò)散作用邊界Example of surface kinetic limitations編輯pptExamples of Kinetics in Nature自然中的動(dòng)力學(xué)范例 Kinetic limitations for dolomite precipitation 白云石沉淀的動(dòng)力學(xué)邊界 Why silicate mineral weathering rates are so much slowe

25、r in nature than in the lab 為什么硅酸鹽礦物在自然環(huán)境中的風(fēng)化速率中比在試驗(yàn)中慢得多編輯pptDolomite Problem關(guān)于白云石的問題Ubiquitous in nature.在環(huán)境中普遍存在Yet, scientists havent been able to participate it at earths surface conditions in the lab目前，科學(xué)家們還不能在實(shí)驗(yàn)室中模擬地球表面環(huán)境形成它Is there a kinetic limitation?是否存在動(dòng)力學(xué)的邊界？CaMg(CO3)2編輯pptDolomite Probl

26、em白云石的問題One hypothesis is that microbes drive dolomite precipitation by reducing sulfate (an inhibitor), and bringing together ingredients for dolomite (Ca, Mg, CO3) on their cell walls:一種假說就是微生物會(huì)減少硫酸鹽（阻聚劑）的含量，進(jìn)而促進(jìn)白云石的沉淀，Work by Judy Mackenzie (ETH)編輯pptComparison between Lab and Field dissolution rates實(shí)驗(yàn)室和野外的溶解速率比較 Dissolution rate depends on mineral surface a