北京大学大学化学先修课程试卷2013年9月.doc

大学先修课程考试（2013年9月） 大学化学 （考试时间：2 小时，卷面总分：100 分，共4道题，考试允许带英汉词典） 一、美国《科学》杂志 2009 年报道了甲烷水化核形成机理的研究文章。请阅读下面文章节选，并回答如下问题。 When methane dissolves in water, a hydrate phase becomes thermodynamically stable at sufficiently low temperatures and high pressures (e.g., for pressures above 80 bar when the temperature is 10°C). The water‐methane liquid mixture is then said to be metastable（亚稳） with respect to the hydrate. The basic mechanism by which a stable phase is formed within a metastable phase is called nucleation（成核）. Under the action of thermal motion, molecular fluctuations give rise to small nuclei of the new phase. The lower free energy of the new phase stabilizes nuclei, but an energetic penalty（能量不利） must be paid to form an interface with the liquid. Below a critical nucleus size（临界核大小）, surface effects are dominant and nuclei redissolve spontaneously（自发地）. Above the critical size, on the other hand, the lower free energy of the bulk stable phase overpowers the interfacial penalty, and nuclei grow, leading to the appearance of a new phase. Beyond these generalities, though, it is not known what a critical hydrate nucleus looks like or how large it is, nor is it understood how a bulk hydrate phase grows from a critical nucleus. Because the rate of nucleation depends exponentially（指数依赖） on the energetic cost of forming a critical nucleus, the lack of detailed knowledge of hydrate nucleation prevents the accurate prediction of hydrate formation kinetics. 1. 请从热力学平衡角度解释为何文章中说：“When methane dissolves in water, a hydrate phase becomes thermodynamically stable at sufficiently low temperatures and high pressures”。 __________________________________________________________________ __________________________________________________________________ ________________________________________________________________。 2. 上述节选中提到水化核形成过程中有两个相互竞争的能量因素可能导致水化核重新溶解或长大，这两个能量因素分别是_____________________________和_______________________________。 3. 文中最后提到，“the rate of nucleation d