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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?
- Can only be in a single phase
- Homogeneous in physical structure
- Homogeneous in chemical composition (correct)
- Consists of a single chemical element
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?
- Three
- Four
- Two (correct)
- One
Which substances can be mixed to form a single liquid phase?
Which substances can be mixed to form a single liquid phase?
- Water and ice
- Oil and water
- Oxygen and nitrogen
- Alcohol and water (correct)
What causes a substance to change its phase at constant pressure?
What causes a substance to change its phase at constant pressure?
What happens to the physical structure of matter during a phase transition?
What happens to the physical structure of matter during a phase transition?
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?
In a P-T Diagram, what does the Triple Point represent?
In a P-T Diagram, what does the Triple Point represent?
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?
What does the Critical Point in a P-T Diagram indicate?
What does the Critical Point in a P-T Diagram indicate?
What is Wet Vapor in thermodynamics?
What is Wet Vapor in thermodynamics?
Which type of phase transition occurs at the Triple Point?
Which type of phase transition occurs at the Triple Point?
What does the term 'Sensible Heat' refer to in thermodynamics?
What does the term 'Sensible Heat' refer to in thermodynamics?
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?
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?
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?
Which phase transition involves the absorption of energy during melting?
Which phase transition involves the absorption of energy during melting?
What is the latent heat of fusion for water at approximately 0 ℃?
What is the latent heat of fusion for water at approximately 0 ℃?
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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