156-7-2影响化学反应速率的因素2

1、第第3节节 反应物浓度与时间的关系反应物浓度与时间的关系一、一、0 0级反应级反应(a)The concentration of the reactant in a zero-order reaction falls at a constant rate until the reactant is exhausted.(b) The rate of a zero-order reaction is independent of the concentration of the reactant and remains constant until all the reactant has be

2、en consumed, when the rate falls abruptly to zero.速率常数的单位与反应级数有关： 一级反应 s1 二级反应 dm3mol1s1 n级反应 dm3(n1)mol1(n1)s1化学反应速率常数k是在给定温度下，各反应物浓度皆为 1 moldm-3时的反应速率，因此也称比速率常数。速率常数是温度的函数。One reactant A decomposes in 1st or 2nd order rate law.Differential rate lawIntegrated rate law dA / dt = kA = Ao k t dA = k A

3、A = Ao e k t or ln A = ln Ao k t d t dA 1 1 A conc at t = k A2 = k t d t A Ao Ao conc at t = 0二、二、1 1级反应级反应AtlnAtA = Ao e k tln A = ln Ao k tt dA = k AA = Ao e k t or ln A = ln Ao k t d tHalf life & k of First Order Decomposition半衰期和速率常数The time required for half of A to decompose is called half

4、 life t1/2.SinceA = Ao e k t or ln A = ln Ao k tWhen t = t1/2, A = AoThus ln Ao = ln Ao k t1/2 ln 2 = k t1/2k t1/2 = ln 2 = 0.693 relationship between k and t1/2Radioactive decay usually follow 1st order kinetics, and half life of an isotope is used to indicate its stability.Evaluate t from k or k f

5、rom t dA 1 1 A conc at t = k A2 = k t d t A Ao Ao conc at t = 0三、三、2 2级反应级反应Dimerization of butadiene is second order:2 C4H6(g) = C8H12(g).The rate constant k at some temperature is 0.100 /min. The initial concentration of butadiene B is 2.0 M. Calculate the time required for B = 1.0 and 0.5 MCalcul

6、ate concentration of butadiene when t = 1, 5, 10, and 30.例子：例子：A 2nd Order ExampleDimerization of butadiene is second order:2 C4H6(g) = C8H12(g).The rate constant k at some temperature is 0.100 /min. The initial concentration of butadiene B is 2.0 M. Calculate the time t required for B = 1.0 and 0.5 MCalculate concentration of butadiene when t = 1, 5, 10, and 30.1 1 = k tBBo1 1 BBo t = kBoB =