This study sought to uncover memorized algorithms and procedures that students relied on in responding to questions based on the particulate nature of matter (PNM). We describe various memorized algorithms or processes used by students. In the study, students were asked to balance three equations of chemical reaction and then draw particulate representations of the compounds in the reactions. Students were then interviewed to uncover their understanding of underlying chemistry, taking note of any memorized algorithms that students were using. In addition to specific algorithms that students used, two trends were apparent from our analysis: (1) students successfully applied algorithms (in operations such as equation balancing) without necessarily understanding why they used the particular operations or processes. (2) Students have memorized processes and ideas which they incorrectly applied. Implications for assessment, research and instruction are also suggested.