The 2nd Law of Thermodynamics states that when energy is converted from one form to another, some is always lost due to , which always increases. (one-word answer; a few different synonymous choices are acceptable)

Enthalpy Difference

Explanation:

The 2nd Law of Thermodynamics states that when energy is converted from one form to another, some is always lost due to difference in the enthalpy of the system, which always increases. Enthalpy may be defined as the amount of energy that is stored. During a chemical reaction, the system will absorb or gives out energy in the form of heat and light. The change in energy during a chemical reaction is due to the difference in the energy amount of reacting species and species that are formed.

Neither model is able to show the reactivity of potassium.