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在化学计算中遇到一定难度的题目或综合题时,往往可以用摩尔或克当量来计算。前者按步就班一步步解出,后者根据当量定律往往可以用比较简捷的方法解出。根据自己实践,发现在化学计算中,往往有这样一种情况:物质之所以气体的体积有变化、质量有变化,其原因就是因为外界条件发生了变化,或者一种物质变成了另一种物质,这种原子换上了另一种元素的原子……。这是化学计算的一种特点:物质质量的差值是由什么条件引起的。根据这一道理,就可以紧紧抓住题目告诉我们的条件中:“物质之所以体积、质量有变化的原因是因为……”这一层含义来进行运算,这就是差值法的原理。这样,使原来计算较为繁复的题目简单化了。这对于培养同学抽象思维能力及综合分析能力也有一定作用。下面举几个例子来说明。
When a problem or a comprehensive problem is encountered in the calculation of a certain degree of difficulty in chemical calculation, it is often possible to calculate the molar or gram equivalent. The former can be solved step by step step by step, and the latter can be solved in a relatively simple and easy way according to the law of equivalents. According to their own practice, it was discovered that in chemical calculations, there is often a situation where the substance has a change in the volume and quality of the gas. The reason is that the external conditions have changed, or that one kind of substance has changed into another. Material, this atom is replaced with another element of the atom... This is a characteristic of chemical calculations: what conditions are the differences in material quality? According to this principle, we can firmly grasp the conditions under which the subject tells us: “The reason why the volume of matter, the reason for the change in quality is because of ...” This is the principle of the difference method. This simplifies the problem of relatively complicated calculations. This also has a certain role in cultivating students’ abstract thinking ability and comprehensive analysis ability. Here are a few examples to illustrate.