评析一道中考压轴题

有一种半导体，其电阻的大小随温度的变化而明显地改变，利用这种半导体材料制成的电阻叫热敏电阻．热敏电阻可以用来测量温度的变化，且反应快，精度高．     

铁与硝酸反应考题归类

铁与硝酸反应的考题是高中化学久考不衰的热点问题．因为这是一个受多种因素影响较为复杂的反应，因此命题眷可以从硝酸的浓度、反应温度、硝酸与铁的相对用量不同等因素变化利用基本概念、氧化还原反应、离子反应、推理计算等原理而设计出许多优秀的试题．本文将对铁与硝酸反应的考题作出归类．     

关注物质鉴别过程中的放热现象

放热现象存在于酸碱中和反应、酸碱的溶解、某些碱性氧化物（如CaO、Na2O）与水的反应等过程中．人的手指具有丰富的神经末梢,对温度的变化比较敏感,如果放热的效应不是很微弱,实验过程中因放热引起的温度变化就可被手的触觉感知,从而有助于人们对某些物质的鉴别．     

三氯苯甲酸的合成

以１，２，４－三氯苯和四氧化碳为原料，通过傅－克反应和水解反应合成２，３．５－三氯苯甲酸．研究了反应温度、时间、催化剂用量等诸因素对产品产率的影响，确定了最佳反应条件．     

影响红花油脂肪酸单甘酯合成的因素

以红花籽油和甘油为原料，在碱催化剂的作用下合成红花油脂肪酸甘油酯，分析了红花油品质对该反应的影响，考察了加入N，N-二甲基甲酰胺溶剂时的浴剂效应以及反应过程中的温度效应、浓度效应．结果发现，反应时间随总反应浓度的减少而同步减少，随总反应浓度的增大而同步增大；在不同的反应温度下，红花油脂肪酸单甘酯浓度随时间延长而增长，其变化的图形呈正抛物线的右半部分；催化剂用量相同时，反应中间体的稳定时间与产率呈正相关性．     

对某些化学试题命题的看法

第6题标准答案为C、D；我认为只能选D．因为有机反应特点之一就是往往伴随有副反应，故写有机反应化学方程式时不用“＝”号，而用“→”号，现题目中所给出的有机反应方程式用的是“→”，故其本身就已向考生暗示它伴随有副反应了．第11题标准答案为D，我认为该题还须加一个条件：在20℃－80℃范围内．因为有的物质在一定温度范围内溶解度随温度变化大，而在另外的温度范围内变化却小，例如苯酚．第14题标准答案为B，这在通常情况下是对的，但若条件为高温、低压，则本题无答案可选，因为生成的NH3全部挥发后，溶液即为氯化钠溶液，H …     

试分析石油裂解的几个问题

本文从热力学角度分析石油裂解的几种反应．阐明了烃分子越大越易断裂，裂解的温度要高于裂化的反应温度，以及裂解过程断链比脱氢容易等事实．探讨了炕烃的断裂方式．这对教学和生产都将带来助益．     

固体超强酸SO42-/TiO2的制备及催化合成苯甲酸异戊酯的工艺研究

以固体超强酸为催化剂，用苯甲酸和异戊醇两种原料，直接酯化合成苯甲酸异戊酯．首先制备固体超强酸SO4^2-／TiO2，然后以此为催化剂进行酯化反应．反映过程中，考察了反应温度，原料配比，催化剂用量，反应时间等酯化反应的影响，由此确定最佳合成工艺条件：反应温度170℃，反应时间3h，异戊醇和苯甲酸摩尔比4：1，催化剂用量2％（以体系总质量计算）．由此条件下，其中苯甲酸异戊酯的收率达87．50％．     

化学反应与温度控制

化学反应与温度控制山东沂南二中（２７６３００）夏立先化学反应离不开一定的温度，温度对化学反应的作用至关重要，通过控制温度，就可控制反应能否发生、反应进行的速度、反应进行的程度、反应进行的方向等等．因此，正确认识、理解、评价温度对化学反应的影响，对学习...     

固体超强酸TiO2／SO4^2-催化合成硬脂酸乙酯

以硬脂酸和无水乙醇为原料，固体超强酸TiO2／SO4^2-为催化剂，催化合成硬脂酸乙酯，考察了不同活化温度对催化剂催化活性的影响，原料醇酸比，反应的时间、催化剂的用量等工艺条件对酯化反应产率的影响，并用正交实验优化出较佳的合成条件，即520℃活化的催化剂催化活性最高．较佳的工艺条件是：乙醇：硬脂酸=9：1，催化剂：硬脂酸=0．09：1，反应温度为83℃，反应时间为8h．硬脂酸乙酯产率可达96．5％．     

Children's understanding of substances,part 1: recognizing chemical change

Arising from a study which explored the development children's concept of a substance (ages 11-14), this two-part paper focuses on the idea of chemical change. Part one considers substance identity and pupils' interaction with the scientific idea of melting and boiling behaviour as a means for identification and the assessment of purity. Evidence is presented which suggests that children do not 'naturally' have a concept of substance identity which allows them to recognize chemical change as a possibility. Instead, their thinking is in terms of the history of samples. The scientific idea of identity led to a confrontation with the idea of chemical change but the pupils were unwilling to accept this phenomenon. The preference was to view the product of a chemical change as a 'mix' of the original substances rather than as a substance in its own right. Implications for teaching are discussed. Part two (in press) goes on to examine the issue of explaining chemical change.     

Children's understanding of substances,Part 2: Explaining chemical change

This is the second part of a paper which focuses on the idea of chemical change (see Johnson 2000). The reported data comes from a study which explored the development of children's concept of a substance (ages 11-14). It examines the use of the ideas of elements, compounds and the bonding between atoms to explain chemical change and the intersection of these ideas with 'basic' particle ideas. Evidence is presented which suggests that the particle ideas were the means by which the pupils came to acknowledge the phenomenon of chemical change, having been unmoved by a macroscopic approach which identified substances by melting and boiling point. Furthermore, a basic particle model in which individual particles still retained the macroscopic properties of the substance was found to inhibit an understanding of chemical change. Findings with respect to a burning candle are reported in a separate section. Important implications for teaching are discussed.     

Grade 12 French Students’ use of a Thermodynamic Model for Predicting the Direction of Incomplete Chemical Changes

The authors of the current chemistry curriculum—implemented in Grade 12 in France—provided a criterion of change allowing prediction of direction of chemical changes and pointed out the difference to be made between experimental facts and models. A study analysing part of the curriculum content and the effects of teaching this content on students’ reasoning was conducted. The content analysis presents the functioning of the thermodynamic model, which highlights the links to be made between the experimental situation and the model when predicting the direction of a chemical change. This functioning specifies the role of the chemical equation and that of the criterion of change (comparing the reaction quotient to the equilibrium constant) and stresses the crucial points that may lead to misunderstandings. Written tests were administered to students after teaching them to determine how they predicted the direction of a chemical change, and whether they made a relevant choice between using the chemical equation and using the criterion of change and a clear distinction between the experimental situation and the thermodynamic model. Few students had a good understanding of the respective roles of the criterion and the chemical equation. A majority used the criterion to predict the direction of chemical changes relevantly, but correct answers were not widespread. Two particular mistakes, the modification of the expression of the reaction quotient and the prediction of a change despite a missing reactant, revealed that students do not properly understand the difference and the relationship between the experimental situation and the thermodynamic model.     

Physical and chemical change in textbooks: An initial view

The concepts of physical and chemical change have been treated in a variety of ways in textbooks. In this study 527 chemistry/science textbooks from a variety of countries and written at different levels of education were examined to see how they dealt with the topic of physical and chemical change. Textbooks have continued to cover this topic for over one hundred years. What evidence do textbooks contain about the purposes and methods of teaching this topic? Is its coverage in textbooks increasing or decreasing? When was physical and chemical change first taught and is it still appropriate to teach this topic? These and other related questions are considered in the paper.     

Contributions of Learning Through Analogies to the Construction of Secondary Education Pupils’ Verbal Discourse about Chemical Change

This article analyzes the relationship between pupils’ level of understanding of the analogies proposed in class while working with a model of chemical change and their competence at constructing a coherent verbal discourse of that model in both its macroscopic and submicroscopic representations. The study participants were 35 pupils in their 3rd year of compulsory secondary education (14–15 years of age) who had been studying chemical change for several weeks in their subject of Physics and Chemistry. The results suggested that the pupils generally understood the proposed analogies quite well, and that a good proportion of them assimilated adequately the verbal discourse inherent in the proposed model of chemical change. There was also a statistically significant association between modeling and analogical thinking. In particular, the pupils with greater understanding of the analogies being considered were also those who tended to show a greater ability to verbalize the model of chemical change and reason with it when solving the tasks they had been set. These results concur with the literature by suggesting that a link exists between analogical thinking and modeling, and that learning with analogies has a positive influence on the construction of the chemical change model.     

量热法测定标准平衡常数的推求

根据标准热力学函数与标准平衡常数的关系，用量热法求算化学反应的标准摩尔焓变和标准摩尔熵变，进一步求算化学反应的标准平衡常数，从理论上进行了推求。     

Using the Science Writing Heuristic Approach to Enhance Student Understanding in Chemical Change and Mixture

This study investigated the effect of the Science Writing Heuristic (SWH) approach on grade 9 students’ understanding of chemical change and mixture concepts. Four intact classes taught by two chemistry teachers from a Turkish public high school were selected for the study; one class was assigned as the treatment group, and the other class was assigned as the comparison group. Students in the treatment group were instructed by the SWH approach, while those in the comparison group were instructed with traditionally designed chemistry instruction. Tests measuring students’ conceptual understanding in the units of chemical change and mixture were administered as pre- and posttest for both groups. At the end of the instruction, semistructured interviews were conducted with 13 students from the treatment group and eight students from the comparison group. ANCOVA results revealed that the SWH approach was superior to the traditional approach on students’ understanding of chemical change and mixture concepts. Interview results indicated that students in the treatment group demonstrated better scientific understanding of chemical change and mixture concepts compared to those in the comparison group.     

催化剂与反应速率及化学平衡关系的论证

文章论证了可逆反应中正逆反应Arrhenius公式内指前因子的比值为一常数,催化剂的存在可降低正逆反应的表观活化能和改变指前因子,但不能改变正逆反应指前因子的比值,进而从化学动力学角度推证了催化剂不影响化学平衡的热力学论断,指明催化剂的催化作用是通过降低表观活化能和改变表观指前因子的协同效应而实现的.     

谈谈△G~0=-RTlnK一式在应用时应注意的一些问题

本文从国际单位制(SI)出发,讨论了化学反应的自由能变化△G~0的单位是什么和依△G~0=-RTlnK一式而得的平衡常数K有无单位的问题。     

农学门类化学实验教学改革的探索与实践

本文就农学门类化学实验中存在的一些实际问题提出了自己的见解,并从如何改变观念使学生正确认识化学实验的重要性、合理安排实验内容、改革探索新的实验教学方法、建立保证实验教学质量的考核体系等方面进行了改革探索与实践.