Chemical kinetics is a highly quantitative content area that involves the use of multiple mathematical representations to model processes and is a context that is under-investigated in the literature. This qualitative study explored undergraduate student integration of chemistry and mathematics during problem solving in the context of chemical kinetics. Using semi-structured interviews, participants were asked to make their reasoning and thinking explicit as they described provided equations and as they worked though chemical kinetics problems. Here we describe the results from our study, which included thirty-six general chemistry students, five physical chemistry students, and three chemical engineering students. Analysis and findings are framed in terms of blended processing, a theory from cognitive science that characterizes human knowledge integration. Themes emerged relating to contexts that were commonly discussed when blending occurred. Variation in the depth and directionality of blending was also observed and characterized. Results provide implications for supporting student problem solving and the modeling of chemical processes.