Which of the following statements/expressions is/are correct?

The internal energy (U) is characteristic of the state of a system, whereby the adiabatic work, W required to bring about a change of state is equal to the difference between the value of U in one state and that in another state, i.e.ΔU=U2-U1=WadThe positive sign expresses that Wad is positive when work is done on the system. If the work is done by the system, Wad will be negative.