The standard heat of formation is the energy change that occurs when 1 mole of a substance is made from its elements in their standard states ( most stable form of the element at 1 bar of pressure and the specified temperature, usually 298 K or 25 degrees Celcius)
E.g for MgCO3
Mg (s) + C (s) + 3/2 O2 (g) = MgCO3
Chemical Compound- a chemical substance consisting of 2 or more different chemically bounded chemical elements with a fixed ratio determining the composition. It is commonly used for electricty
You can know which one has more thermal energy by testing the temperature, if it is warmer the more energy it has because the particles are going faster than they would if it was cold. because, when its cold the particles slow down until they are so cold they are frozen. (ice).