The design and use of a chemistry practice exam instrument that includes a measure for student mental effort is described in this paper. Use of such an instrument can beneficial to chemistry students and chemistry educators as well as chemical education researchers from both a content and cognitive science perspective. The method for calculating and representing cognitive efficiency in different chemistry categories at both the student-level and classroom-level is described. In addition, explanation of the information available and potential benefits to each of the target populations is discussed with respect to instrument use.