In this work, we examine whether tenth-grade high school students (N = 197, age 15- 16) as well as first-year university chemistry students (N = 77, age 18-19) can make the connection between chemical reactions and chemical phenomena. We used nineteen physical and chemical phenomena, and asked the students at one stage to distinguish physical from chemical phenomena, and at another stage to state in which cases one or more reactions occur. Students can be categorised into two distinct groups. One group includes those who do not always identify chemical phenomena with reaction(s), while the other group includes those who are successful in that distinction. Further, the students of the first group can be divided into two subgroups: (a) those who perform better in identifying the chemical phenomena; (b) those who perform better in identifying the reactions. A differentiation of chemical changes into natural and man-caused processes seems to be operating, at least with Greek students. On the other hand, students may be intuitively viewing chemical reactions as fairly simple processes, which can be expressed by means of chemical equations. Finally, it might be preferable to group (i) changes of physical state and phase, and (ii) solutions, in a separate category (physicochemical changes). [Chem. Educ. Res. Pract.: 2003, 4, 31-43]