This research aimed to explore the conceptual structure of chemical equilibrium in upper-secondary school students using factor analysis. Research on chemistry education has shown that chemical equilibrium is an important but difficult-to-understand topic. Exploring the conceptual structure of chemical equilibrium among students will help chemistry researchers and educators to conduct more targeted teaching practices. Based on a survey of chemistry research and teaching practice experts, a high-quality concept pool composed of 24 relevant concepts was developed. Next, a survey involving a total of over 700 twelfth-grade students from five upper-secondary schools was conducted, and a factor analysis was utilized to determine the conceptual structure. The results showed that a three-factor model and a five-factor model with 15 relevant concepts were all accepted as the conceptual structure for students. The new form of conceptual structure in this research helps understand the features and categories in students’ latent organization of concepts. Also, it may be revealed that factor analysis can be utilized as an approach to exploring students’ conceptual structure. Keywords: chemical equilibrium, chemistry education, conceptual structure, factor analysis

Chemical equilibrium is so important domain knowledge in chemistry that the corresponding organisation of concepts in students has been an interesting but unsolved issue. A deeper understanding of how students organise the relevant concepts in long-term memory is beneficial to develop more targeted teaching practices. This research utilized the reaction time technique as a new approach to exploring upper-secondary school students’ organisation of concepts regarding chemical equilibrium. A category judgment task involving 247 Chinese twelfth-grade students from two upper-secondary schools was conducted. The results showed that a significant difference was between the reaction time of concept dimensions. The mean reaction time of the dimension ‘reversible reaction’ was the shortest, but the dimension ‘representation of state’ had the longest mean reaction time. Next, there was no significant difference in the organisation of concepts between students studying chemistry at different levels of academic achievement. These findings provide a new and essential picture to deeply understand the organisation of concepts regarding chemical equilibrium and help focus on the relations between some relevant concepts. This research represents that the reaction time technique can be utilized in the research on organisation of science concepts. Keywords: category judgment task, chemical equilibrium, organisation of concepts, reaction time