Although students' misconceptions about the concept of chemical equilibrium has been the focus of numerous investigations, few have investigated students' systematic errors when solving equilibrium problems at the college level. Students (n=189) enrolled in the second semester of a first year chemistry course for science and engineering majors at a private university in New York State were studied to: (1) identify students' conceptual chemical errors and systematic mathematical errors when solving chemical equilibrium problems; and (2) to investigate the relationship between students' logical thinking ability and their performance on the kinetics and chemical equilibrium problems. Data was collected using a student demographics questionnaire, the Test of Logical Thinking, and students' responses to three chemical equilibrium problems and one chemical kinetics problem. Content analysis of the conceptual chemical and mathematical errors led to four conclusions: (1) students did not understand the relationship between experimental results and the rate of reaction; (2) students' misconception that an arithmetic relationship existed between concentrations of reactants and products led to a mathematical rather than a chemical solution to one problem; (3) many students seemed to have an overgeneralized definition of bases; and (4) students relied on using learned algorithms to solve problems. Contains 22 references. (MDH)