If the liquid water at 25 degree C 1 atm is set as reference

If the liquid water at 25 degree C, 1 atm is set as reference, i.e., internal energy U=0, is U>0 or U

Solution

3) The Internal energy of any substance is composed of kinetic, potential and vibrational energies of the substance.

i) Saturated steam at 1 atm is at 100^oC, with an increase in temperature the kinetic energy of the substance increases. As the substance changes from liquid to vapor, the vibrational energy also increases. Thus the Internal energy for saturated steam is greater than the reference. i.i U>0

ii) Ice at 1 atm is at 0^oC, Phase change from liquid to solid reduces the vibrational energy and temperature drop reduces the kinetic energy. hence the internal energy of ice will be less than the reference . i.e. U<0