phase transformations - vocabulary phase allotropes phase transitions phase diagram
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Phase Transformations - Vocabulary Phase Allotropes Phase Transitions Phase Diagram Normal vs Standard Transition Temperatures Critical Temperature Triple Point. Phase and Allotropes Phase: Uniform in physical state and chemical composition - PowerPoint PPT PresentationTRANSCRIPT
Phase Transformations - Vocabulary
• Phase
• Allotropes
• Phase Transitions
• Phase Diagram
• Normal vs Standard Transition Temperatures
• Critical Temperature
• Triple Point
Phase and Allotropes
Phase: Uniform in physical state and chemical composition
Mathematically, a phase has 1 equation of state.
Allotrope: One of at least two different crystalline or molecular structures of a substance
Examples: Ice, Phosphorous (White and Black), Carbon (Graphite and Diamond)
Phase Transformations - Vocabulary
Phase
Allotropes
• Phase Transitions
• Normal vs Standard Transition Temperatures
• Phase Diagram
• Critical Temperature
• Triple Point
Phase Transitions
Spontaneous conversions from one physical state (phase) to another. The phases are in equilibrium during a phase transition.
What does that mean about S?
What about G?
Transition Temperature
The temperature, AT A GIVEN PRESSURE, where a phase transition occurs.
Phase Diagram
Normal Melting Point
Standard Melting Point
Phase Diagrams
Phase diagrams give us a general idea about phase stability….
But they don’t tell the whole story.
Example: Allotropes of carbon
C(diamond) C(graphite)
Gibbs Free Energy
Diamond
Graphite
2.9 kJ/Mol
Phase Diagram
Normal Melting Point
Standard Melting Point
Super Critical Fluid
Critical Point
Critical Point
Tc (K) Pc (atm)
CO2 304.2 72.85
Br2 584 102
H2O 647.4 218.3
O2 154.8 50.14
CH4 190.6 45.6
CO2
H2O
Ice-I and liquid water boundary has a negative slope
There are 6 different types of Ice (7 triple points)
There is no such thing as Ice IV
Ice VII isn’t shown on this diagram
Helium
Gas and solid never coexist
Two allotropes (body centered cubic and hexagonal closed packing)
Two liquid forms
• A superfluid flows without any viscosity
Quantum effects are relevant 3He and 4He have different phase diagrams.
Chemical Potential ()
Is a quantitative measure of a substance’s ability to bring about change.
For a pure substance, is the potential to bring about physical change (a phase change).
Do we have a quantity that sort of describes that kind of potential?
Entropy is the driving force of the universe.
Molar Gibbs free energy is the definition of for a pure substance.
Is going to help us quantify how the system changes under the given conditions.
Chemical Potential
Any system in equilibrium must have the same chemical potential throughout the entire system
The chemical potential of a solid phase changes with T differently than that of the liquid phase. for a liquid changes at a different rate than that of a solid or liquid.