Water Vapor Property Diagrams for Phase-Change Processes

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Questions and Answers

What is a defining characteristic of a pure substance?

Homogeneous in chemical composition

How many phases can a system of liquid water and water vapor (steam) contain?

Two

Which substances can be mixed to form a single liquid phase?

Alcohol and water

What causes a substance to change its phase at constant pressure?

Absorption or rejection of latent heat Signup and view all the answers

What happens to the physical structure of matter during a phase transition?

It changes abruptly Signup and view all the answers

When can a mixture of two or more phases of a pure substance still be considered a pure substance?

When the chemical composition of all phases is the same Signup and view all the answers

In a P-T Diagram, what does the Triple Point represent?

The temperature and pressure at which solid, liquid, and vapor co-exist in equilibrium Signup and view all the answers

Which region of the property diagram represents a saturated gas phase of water?

Vapor or Dry Vapor region Signup and view all the answers

What does the Critical Point in a P-T Diagram indicate?

The highest temperature and pressure at which liquid and vapor co-exist in equilibrium Signup and view all the answers

What is Wet Vapor in thermodynamics?

A combination of saturated vapor and saturated liquid Signup and view all the answers

Which type of phase transition occurs at the Triple Point?

All three phases co-existing in equilibrium Signup and view all the answers

What does the term 'Sensible Heat' refer to in thermodynamics?

Heat required to change the temperature of a substance without a change in phase Signup and view all the answers

What is the phase transition when a substance changes from a gas to a solid?

Deposition Signup and view all the answers

Which type of heat is involved in changing the temperature of a substance without changing its phase?

Sensible heat Signup and view all the answers

What is the process called when a substance changes directly from a solid to a gas?

Sublimation Signup and view all the answers

Which phase transition involves the absorption of energy during melting?

Fusion Signup and view all the answers

What is the latent heat of fusion for water at approximately 0 ℃?

334 kJ/kg Signup and view all the answers

During which phase transition is energy released as a substance changes from a gas to a liquid?

Condensation Signup and view all the answers

Study Notes

Degrees Superheat

Superheat is defined as the difference between the saturation temperature and the actual temperature of the substance at a given pressure.
Example: At 1 atm, the superheat of water is 50°C (150°C - 100°C).

Property Diagrams for Phase-Change Processes

P-T Diagram (Phase Diagram): shows the relationship between pressure and temperature during phase-change processes.
Critical Point: the highest temperature and pressure at which liquid and vapor co-exist in equilibrium (for water: 22.06 MPa, 217.7°C, 647.096 K).
Triple Point: the temperature and pressure at which solid, liquid, and vapor phase of a substance co-exist in equilibrium (for water: 0.6117 kPa, 0.01°C, 273.16 K).

Types of Property Diagrams

T-v Diagram: shows the relationship between temperature and specific volume.
P-v Diagram: shows the relationship between pressure and specific volume.
T-s Diagram: shows the relationship between temperature and entropy.
h-s Diagram (Mollier Diagram): shows the relationship between enthalpy and entropy.

Thermodynamic Surface

P-v-T Surface: a three-dimensional diagram that shows the relationship between pressure, volume, and temperature.

Phase Transition

Change of Phase at Constant Pressure:
- Fusion/Melting: solid to liquid.
- Freezing/Solidification: liquid to solid.
- Vaporization/Evaporation: liquid to gas.
- Condensation: gas to liquid.
- Sublimation: solid to gas.
- Deposition: gas to solid.

Latent Heat and Sensible Heat

Latent Heat: the amount of heat absorbed or released by the substance during a phase-change process at constant temperature.
Sensible Heat: the amount of heat required to change the temperature of the substance without changing the phase of the substance.
Latent Heat of Fusion: the amount of energy absorbed during melting (equivalent to the amount of energy released during freezing).
Latent Heat of Vaporization: the amount of energy absorbed during vaporization (equivalent to the energy released during condensation).

Pure Substance

A substance that is homogeneous and invariable in chemical composition throughout.
A mixture of various chemical elements or compounds can also qualify as a pure substance as long as the mixture is homogeneous.

Phase

A quantity of matter that is homogeneous throughout in both chemical composition and physical structure.
A system can contain one or more phases.

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