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Questions and Answers
What is a defining characteristic of a pure substance?
What is a defining characteristic of a pure substance?
How many phases can a system of liquid water and water vapor (steam) contain?
How many phases can a system of liquid water and water vapor (steam) contain?
Which substances can be mixed to form a single liquid phase?
Which substances can be mixed to form a single liquid phase?
What causes a substance to change its phase at constant pressure?
What causes a substance to change its phase at constant pressure?
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What happens to the physical structure of matter during a phase transition?
What happens to the physical structure of matter during a phase transition?
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When can a mixture of two or more phases of a pure substance still be considered a pure substance?
When can a mixture of two or more phases of a pure substance still be considered a pure substance?
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In a P-T Diagram, what does the Triple Point represent?
In a P-T Diagram, what does the Triple Point represent?
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Which region of the property diagram represents a saturated gas phase of water?
Which region of the property diagram represents a saturated gas phase of water?
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What does the Critical Point in a P-T Diagram indicate?
What does the Critical Point in a P-T Diagram indicate?
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What is Wet Vapor in thermodynamics?
What is Wet Vapor in thermodynamics?
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Which type of phase transition occurs at the Triple Point?
Which type of phase transition occurs at the Triple Point?
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What does the term 'Sensible Heat' refer to in thermodynamics?
What does the term 'Sensible Heat' refer to in thermodynamics?
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What is the phase transition when a substance changes from a gas to a solid?
What is the phase transition when a substance changes from a gas to a solid?
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Which type of heat is involved in changing the temperature of a substance without changing its phase?
Which type of heat is involved in changing the temperature of a substance without changing its phase?
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What is the process called when a substance changes directly from a solid to a gas?
What is the process called when a substance changes directly from a solid to a gas?
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Which phase transition involves the absorption of energy during melting?
Which phase transition involves the absorption of energy during melting?
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What is the latent heat of fusion for water at approximately 0 ℃?
What is the latent heat of fusion for water at approximately 0 ℃?
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During which phase transition is energy released as a substance changes from a gas to a liquid?
During which phase transition is energy released as a substance changes from a gas to a liquid?
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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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Description
Study the variations of properties during phase-change processes using property diagrams, specifically the P-T Diagram. Learn about critical points, such as the highest temperature and pressure at which liquid and vapor co-exist in equilibrium.
