What do you mean by change in internal energy?
Please elaborate and also how it is equal to delta u

Internal energy (U) is basically what it sounds like: How much energy a system has. This includes kinetic and potential energy and can be increased by heating or doing work on a system or exchanging mass.


The U term can be interpreted as the energy required to create the system, and the pV term as the energy that would be required to "make room" for the system if the pressure of the environment remained constant. When a system, for example, nmoles of a gas of volume V at pressure p and temperature T, is created or brought to its present state from absolute zero, energy must be supplied equal to its internal energy U plus pV, where pV is the work done in pushing against the ambient (atmospheric) pressure.

The first law of thermodynamics states that the change in internal energy of a system \Delta UΔUdelta, U equals the net heat transfer into the system Q,plus the net work done on the system W. In equation form, the first law of thermodynamics is,
\Large \Delta U=Q+WΔU=Q+W
\Delta UΔUdelta, U is the change in internal ener
Gy of​​​​​ the system. Q is the net heat transferred into the system—that is, Q is the sum of all heat transfer into and out of the system. Wis the net work done on the system.
So positive heat Qadds energy to the system and positive work W adds energy to the system. This is why the first law takes the form it does,
Delta U=Q+W
delta, U, equals, Q, plus, W. It simply says that you can add to the internal energy by heating a system, or doing work on the system.