Question

What is meant by internal energy of a system? State the first law of 

thermodynamics in its differential form. Write it for isothermal, adiabatic and 

isochoric changes.

Answer 1

$\bigstar$

$\bull$ Internal energy is NOT all the energy in the system,

$\bull$ it is the kinetic and potential energy associated with the random motion of the molecules of an object.

$\bull$ If you heat an object, you will increase its internal energy.

$\bigstar$ The first law states that internal energy changes occur only as a result of heat flow and work done.

$\boxed{ dU = δQ + dW}$

U (or alternatively E) represents the internal energy of the system. So dU (or dE) represents its differential.

$\boxed{dQ = dE + dw}$

Isothermal Process:

$\boxed{q+W=0}$

adiabatic process

$\boxed{U= -W}$

isochoric process

$\boxed{ Q= U}$