Heat! A word that is SO commonly misunderstood.

The word heat is vastly misunderstood by the common public and peers of mine studying physics.  I always have to say something when someone says "Delta Q is equal to zero." There is no delta Q! Delta Q doesn't make any sense! (For anyone reading this that isn't mathematically inclined, which I don't know how you got here, delta Q means the change in the amount heat from one time to another.)

The reason behind this is because heat is not a state function. An example of a state function would be internal energy.  As an example, if you have a hot cup of water and a cold one, the hot cup has more internal energy than the colder cup. After a certain amount of time, the hot cup will lose internal energy as it cools, thereby having a specific delta U. (U is internal energy).  This is because at one time, the cup of water possessed a discrete amount of energy, and after a certain amount of time, some of that energy dissipated into the surroundings and now it has less energy.  (Internal energy is defined by the atomic motions of the substance.  When you heat something up, the molecules start to oscillate like crazy.  Internal energy is a measure of these motions, which include but are not limited by, translation, rotation, oscillation, nuclear, ect.)  In fact, when you integrate using heat as the differential, you cannot use a straight dQ, it must be δQ because the integral depends on the path not the state conditions!

This is where the misunderstanding comes in, an object cannot possess heat.  Heat is defined as the transfer of energy, not the amount!  Therefore it is impossible for an object to possess heat because heat is a measure of how much energy is entering or leaving the system.  When the hot water is cooling, the internal energy is being converted into heat because it is leaving the system.  (The system in this case being what is inside the cup.)  You can feel this heat with your hand if you place it over or on the cup.

Sometimes I find that in order to explain something I will purposely use the word heat incorrectly for someone who does not know Physics.  The logic behind this is that they will understand what I am trying to say better than if I were to use internal energy, and then have to explain why the word "heat" is inappropriate.

So! An object cannot possess heat, and delta Q makes no sense!