1. The problem statement, all variables and given/known data Explain why the number of modes per particle increases with increasing temperature for all gases (except monatomic gases). 2. Relevant equations 3. The attempt at a solution I am trying to use an energy argument but to be honest, I don't understand the excited state vs rest state stuff in this context. My answer would be: increasing temperature by definition increases the average kinetic energy of the substance and also increases the energy in each existing mode. If the substance has more energy, it can more easily navigate between its excited and ground state which (somehow) leads to the ability to access more modes.