In one of the statements of thermodynamics first law it states that the total internal energy of an isolated system is constant but isolated system means adiabatic system in which Delta u is equals to zero. I just didn't get that?

Mar 1, 2018

An adiabatic process is one in which no net heat is transferred by the process.

Explanation:

We know that in thermodynamics it is very common to either generate or absorb heat. The other variables include volume, temperature and pressure.

An example of a common process is if pressure is decreased, we know that temperature will increase because the molecules of the gas are closer together and will interact more, meaning there will be more friction and the temperature will increase.

Another process that results in lower temperature is if the volume of the gas remains the same, but the volume is increased. Therefore the gas molecules will not interact as often, there is less friction and kinetic energy and the temperature will decrease.

So, imagine a situation where the various variables all change, but they change in such a way that the net result is heat is neither added to or removed from the system. That is an adiabatic process.