Understanding the role of energy in chemical systems is critical to understanding and explaining chemical phenomena. However, research has shown that energy concepts are difficult for students, even at the college level. In order to support students’ understanding of energy in chemical systems, our current work seeks to refine a learning progression for energy in the context of a reformed undergraduate general chemistry curriculum, Chemistry, Life, the Universe and Everything (CLUE). Our previous work has used semi-structured interviews to investigate students’ understandings of the connections between energy ideas at the macroscopic and microscopic levels across a variety of contexts. Of interest in the current work are how students represent and explain the process of solution formation and the connections between temperature changes (at the bulk level) and interactions, energy transformation, and energy transfer (at the atomic-molecular level). Here we present a redesigned formative assessment activity and an analysis of students’ responses to formative and summative assessment items; implications for assessment design and teaching resulting from analysis across multiple semesters will also be discussed.