Final answer:
Water's enthalpy at specific conditions cannot be calculated without steam tables or thermodynamic charts. At 200 ℃ with a specific volume of 0.9 m^3/kg, it suggests a superheated vapor state with a high enthalpy. At 100 ℃ and 0.7 bar, if boiling, enthalpy includes the sensible heat plus latent heat of vaporization at 0.7 bar.
Step-by-step explanation:
Enthalpy Calculation for Water
To determine the enthalpy (h) for water at a given temperature and specific volume or pressure, we would typically use steam tables or thermodynamic charts because these properties depend on the phase of water (liquid, vapor, or a mixture). However, without these resources, we can only provide a qualitative explanation based on the provided scenarios and fundamental principles.
(a) For water at 200 ℃ with a specific volume of 0.9 m^3/kg, this condition suggests water is in a superheated vapor state as the specific volume is much higher than that of liquid water at the same temperature. The enthalpy would be higher than the enthalpy of vaporization at 100 ℃ due to additional heat required to reach 200 ℃ and to expand to a specific volume of 0.9 m^3/kg.
(b) For water at 100 ℃ and a pressure of 0.7 bar, the enthalpy is slightly complex to calculate without a chart since this is close to the boiling point of water under atmospheric pressure. If the water is boiling, the enthalpy would include the heat required to raise the water from reference temperature to 100 ℃ plus the latent heat of vaporization at 0.7 bar (which would be somewhat lower than at 1 bar).
Note that to provide an exact value, one would need to reference appropriate property tables or equations of state that correspond to the particular substance and conditions given.