Question

2 kg of water exist initially as a vapor and liquid at 90 degrees C in a rigid container of volume 2.42 m^3 (a) at what pressure is the system? (b) what is the quality of the system (c) the temperature of the container is raised to 100 degrees C. what is the quality of the system and what is the pressure? what are the dH and dU at this point relative to the initial state? (d) as the temperature is increased, at what temperature and pressure does the container contain only saturated vapor? what is the dH and dU at this point to the initial state? (e) make a qualitative sketch of parts (a) through (d) on a P-V diagram, showing the phase envelope.

Answer 1

Values:

• Latent heat (Lv) of vaporization: L_v= 2.26x10⁶ J.kg^-1 (for water)
• Specific heat (Ce) of water: 4.182 J.g^-1°C^-1
• Volume (V): V=2.42 m³ (flask)
• Mass (H₂O): M=2 kg = 2000 g (for water)
• Molar Mass (Fw): Fw= 18 g.mol^-1 (for water)
• Initial temperature (Ti): T_i= 90°C = 363.15 K
• Ideal gas constant (R): R = 8.314 J.mol^-1.K^-1 = 0.0821 atm.L.mol^-1.K^-1

Expressions:

• Ideal Gas:
• Latent Heat:
• Heat:
• Work (W):
• Internal Energy (dU):
• Enthalpy (dH):

Process:

a) Determine the initial pressure system.

-------------------------------------------------------------------------------------------------------------------------------------------------------

b) Latent heat of vaporization.

-------------------------------------------------------------------------------------------------------------------------------------------------------

c) Heat to temperature change of 90°C to 100°C, dU and dH.

-------------------------------------------------------------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------------------------------------------------------------

d) Final Pressure.

-------------------------------------------------------------------------------------------------------------------------------------------------------

e) Make a qualitative sketch of parts (a) through (d) on a P-V diagram, showing the phase envelope

**Changing the state of matter, the state variables (pressure, volume and temperature should not change), but keep reaching the same stage, then the state variables are no longer constant.