Which best describes the difference between internal and thermal energy? Internal energy is the total potential energy in a substance, and thermal energy is the total kinetic energy in a substance. Thermal energy is the total potential energy in a substance, and internal energy is the total kinetic energy in a substance. Internal energy is the total potential and kinetic energies in a substance, and thermal energy is the part of internal energy that can be transferred to another substance. Thermal energy is the total potential and kinetic energies in a substance, and internal energy is the part of internal energy that can be transferred to another substance