The use of variation theory to improve student understanding of reaction rate through scientific investigation

Abstract

The reaction rate of a chemical process, and the factors that affect it, is an important concept in the secondary school chemistry curriculum. A number of studies have indicated that students have different conceptions of the reaction rate phenomenon, e.g. that volume is an influential factor. The way in which the teacher structures the lesson content and the students experience the lesson is important in helping students to develop appropriate conceptions.

This study explores the efficacy of using variation theory as a pedagogical tool to improve student understanding of chemical reaction rates at the Secondary 4 level through group-based scientific investigation. A design-based research approach with a pretest and posttest was chosen, and phenomenography and variation theory were adopted as the theoretical framework. Learning is defined as a change in the way of experiencing something. What is to be learnt is defined as the “object of learning”, and aspects that are crucial to appropriating the object of learning are defined as “critical aspects”. To bring out the critical aspects that are to be discerned by students, certain patterns of variation, namely, generalization, contrast, separation and fusion, must be constituted.

Two Secondary 4 chemistry classes in the same school were taught by one teacher. Lessons comprised three sections: a single period for introduction, a double period for experimentation and a single period for debriefing. The two classes were taught in the same way during the introduction and experimentation, but different debriefing sequences were used after the students’ experimental work. During the introduction and experimentation, “separation” was employed to help students develop a fair test concept and design an experiment to follow the progress of a chemical reaction. During experimentation, they were guided in how to discern the factors that affect two aspects of a reaction, i.e. the reaction rate and amount of products formed. In the debriefing session of the pilot and main studies, different “sequences of factors” and “sequences of aspects” were followed, respectively. Comparison was made between the pretest and posttest to trace students’ understanding of the reaction aspects. The quantitative data were analysed and triangulated with the post-lesson interview data and verbatim lesson record. The students’ learning outcomes showed that there had been substantial improvement in understanding of the skills and concepts involved, with the gap between the low- and high-score groups narrowing. A specific debriefing sequence was found to be conducive to learning. Further, discussing the interrelated factors tested in the experimental conditions consecutively and separating the two reaction aspects while fusing the factors appeared effective in highlighting the part-part and part-whole relationships. Here, “whole” refers to a reaction consisting of the “parts” constituted by the reaction rate and amount of products which in turn depend on various factors.

The findings of this study suggest that variation theory is a powerful pedagogical tool in improving the understanding of students of lower academic ability. They thus have important implications for the planning of teaching-learning sequences in practical science lessons, particularly in scientific investigations that involve different task-pool results.