When selecting classes for the next semester, the discussion centers on the choice between calculus 3, thermodynamics, and quantum chemistry. While calculus 3 is not a requirement for the major, both thermodynamics and quantum chemistry are essential. Participants suggest that thermodynamics is more universally applicable in chemistry and requires less advanced math compared to quantum chemistry. Some emphasize the importance of having a solid math foundation, recommending courses like calculus 3, linear algebra, and differential equations for a better understanding of physical chemistry concepts. However, others argue that it's possible to learn necessary math skills concurrently with chemistry courses. Group theory is mentioned as beneficial for quantum chemistry, but its prerequisite, an introductory course to proofs, may complicate scheduling. Overall, the consensus leans towards prioritizing thermodynamics and considering additional math courses for a deeper comprehension of the material.