This study explored the impact of oxidation-reduction reaction problem difficulty on university students' cognitive load using event-related potentials (ERPs). Forty-eight balanced low and high difficulty problems were designed. Fifteen undergraduate students majoring in chemistry (8 females and 7 males) participated in the study. Results demonstrated significantly increased reaction time, significantly decreased accuracy, and highly significantly elevated subjective effort as task difficulty intensified. ERP analysis revealed significant differences in N200, P300, and N400 amplitudes between easy and difficult problems, indicating increased demands on control, working memory, and in-depth processing under high load. The study provided physiological evidence supporting cognitive load theory and offered implications for optimizing oxidation-reduction reaction teaching. The findings bridged the gap between cognition and education, suggesting potential avenues for improving chemistry education through cognitive load management.