一、基本学情及教学重难点分析学生在学习化学之前,已经了解到一些物质变化(物理变化和化学变化)的事例。例如,知道铁在潮湿的空气中易生锈,水能结冰或变成水蒸气,燃烧,植物的光合作用等。但是他们并不清楚这些变化的区别和联系。由于学生刚刚开始学习化学,原子、分子的科学概念还没有引入,因此不适宜从微观角度认识物质的变化,判断物质发生的变化是物理变化还是化学变化的依据应为是否有新物质 First, the basic knowledge and teaching difficult analysis of students before learning chemistry, we have learned some material changes (physical changes and chemical changes) examples. For example, iron is known to rust in humid air, water can freeze or turn into water vapor, burning, and plant photosynthesis. But they do not know the difference and connection between these changes. As students have just started to learn the concepts of chemistry, atom and molecule, they have not been introduced yet. Therefore, it is not suitable to recognize the change of matter from the microscopic point of view, and to judge whether the change of matter is a physical change or a chemical change.