Students' understanding of chemical reaction

Students from the 7th and 8th grades at the upper stage of comprehensive school, first-year senior secondary school, and a first-year general chemistry course at university were asked to describe the concept of chemical reaction. Respectively, 14%, 74%, 25% and 59% of the students gave responses that included at least one of the components which point to sound understanding, namely reorganization of atoms, breaking and reformation of bonds, changes in physical or chemical properties. The students had difficulties in the usage of terms such as substance and atom. Very few of the senior secondary (6%) and university (14%) students were able to describe properly the meaning of chemical reaction. The results contribute to a clarification of why teachers experience difficulties in instructing these students in the difference between chemical and physical changes.