ln a study of the properties of a liquid, a 2-kg sample of liquid was heated at a constant pressure of 1 atm from 500 to 600 K. The density of the liquid is 608 and 590 kg/m3 at the initial and final states, respectively. An energy input as heat of 42 kJ was required. Determine the difference in the specific internal energies between the initial and final states (kJ/kg).