Which statement about the physical change of liquid water boiling into steam is true? A The heat added represents an energy change. B The action cannot be reversed. CThe steam cannot conserve mass. The weight lost represents a mass change.

The bond energy for the van der waals bond between two helium atoms is 7.9×10−4ev. assuming that the average kinetic energy of a helium atom is (3/2)kbt, at what temperature is the average kinetic energy equal to the bond energy between two helium atoms