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(A) Calculate the specific heat capacity at constant volume of water vapor, assuming the nonlinear tri-atomic molecules has three translational and three rotational degree of freedom and that vibrational motion does not contribute. The molar mass of water is 18 g/mol.(B) The actual specific heat capacity of water vapor at low pressure is about 2000 J/kg*K. Compare this with your calculation and comment on the actual role of vibrational motion.he molar mass of water is 18 g/mol. (B) The actual specific heat capacity of water vapor at low pressure is about 2000 J/kg*K. Compare this with your calculation and comment on the actual role of vibrational motion.
The principle of energy conservation states that the total energy in the lower-pressure state must equal the total energy in the higher-pressure state. 1  Therefore, the amount of heat in the flash steam and condensate must equal that in the initial condensate of 671 kJ. Steam tables give the following information: 1  Total enthalpy of saturated water at atmospheric pressure (hf) = 419 kJ/kg. 2  Total enthalpy in saturated steam at atmospheric pressure (hg) = 2 675 kJ/kg. 3  Therefore, at the lower pressure state of 0 bar g. 4  Total enthalpy in the water = 0.888 kg x 419 kJ / kg = 372 kJ (A)