Question

what is chamge in internal energy in thermod physics. is it final - initial or opposite? ​

Answer 1

Answer:

Any work or heat that goes into or out of a system changes the internal energy. However, since energy is never created nor destroyed (thus, the first law of thermodynamics), the change in internal energy always equals zero. If energy is lost by the system, then it is absorbed by the surroundings.

Answer 2

We cannot measure the internal energy in a  system. we can only determine the change in internal energy.

Explanation:  In thermodynamics, the internal energy of a system is the energy contained within the system. it is the energy necessary to create or prepare the system in any given state.

The change in internal energy can be positive or negative (as can the heat and the work). the change is defined as the final internal energy minus the initial internal energy.

         ΔU = $U_{f}-U_{i}$

so the negative change means the final energy is lower than the initial energy