Answer to Question #2502 in Molecular Physics | Thermodynamics for sana
Why can heat be conducted through solids, liquids and gases but not through vacuum?
Heat(or thermal energy in transit) is the part of the total, internal energy of a thermodynamic system or sample of matter that results in the system's temperature.
Microscopically, the thermal energy is the kinetic energy of a system's constituent particles, which may be atoms, molecules, electrons, or particles in plasmas. It originates from the individually random, or disordered, motion of particles in a large ensemble.
From the above definition we can see that heat micriscopicaly is the energy of particles (atoms,molecules etc.). And vacuum is defined as a volume of space that is essentially empty of matter.The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in practice. So whereas there are no particles in vacuum , there are no units those could carry heat, so to speak.
Obviously heat can be conducted through solids, liquids and gases, because all the substances mentioned are constructed with particles.