新103第3章化学动力学基础技术分析.ppt

Chemical Reaction Rate 化学反应速率 化学反应速率属化学动力学范畴。像物理学中的速度一样反应速率的单位为单位时间内参与反应的物种浓度的变化。 日常生活中化学反应快慢的尺度，例如，煤气灯的燃烧，炸药的爆炸，酸碱中和均在瞬间完成。钢铁腐蚀，水泥的水化则慢得多。 Chemical Reaction Rate 化学反应速率 根据IUPAC的规定， 化学反应速率是单位时间(秒、分钟、小时)内的反应进度. The expression of chemical rate化学反应速率表达式 例如： 2H2(g) + O2(g) == 2H2O(g) 当 ? = 0.5 mol时, 表示 1 mole 的氢气与0.5 mole的氧气反应形成 1 mole 气态水. The reaction rate can be expressed as Rate under constant volume恒容速率 When the reaction happens in constant volume, the reaction rate can be expressed as: 恒容时反应速率可表示为, where cB is the concentration of species B, ?B is the stoichiometric number of species B. And the reaction rate is expressed either in mol?L?1?s?1 or mol?L?1?min?1. 反应速率的单位是mol?L?1?s?1或mol?L?1?min?1。 Instantaneous rate and average rate 瞬时速率与平均速率 It should be noted that the reaction rate implies the instantaneous rate. 值得注意的是: 反应速率意指瞬时速率。 Normally, we use average rate. 实际上，用平均速率。 For instance, 3H2(g) + N2(g) == 2NH3(g) the rate is, Factors Affecting the Chemical Reaction Rate—concentration 影响化学反应速率的因素—浓度 Daily experiences tell us that increase in concentrations of the reactants will increase the reaction rate. The rate increase varies with the chemical reactions 反应物浓度增加，正反应速率加快。反之，增加产物的浓度，逆反应的反应速率增加。不同的化学反应，反应速率随浓度变化的关系是不同的。 Rate expression 速率表达式 The relation between reaction rate and the concentrations of reactants can be given by a mathematical equation called rate expression. 我们总能找到一个数学式来表示反应速率和浓度之间的关系，该数学式称速率表达式。 But, this expression must be evaluated only through experiments. 但是速率表达式只能由实验获得。 For a reaction, aA + bB == cC + dD the rate expression will have the formula, v = k?{c(A)}m? {c(B)}n Total reaction order 总反应级数 where k = rate constant, c(A) = concentration of reactant A, c(B) = concentration of reactant B, and m = order of reaction for reactant A, and n = order of reaction for reactant B. k为速率常数， c(A)是反应物A的浓度。m是反应物A的反应级数， c(B)是反应物B的浓度，而n是反应物B的反应级数. T