24 Questions
What is the number of degrees of freedom for the system ice-water-vapour at the triple point?
0
What is the effect of an increase in pressure on the melting point of ice?
It decreases the melting point
What is the condition for a system to be monovariant?
It has two phases and one component
What is the significance of the triple point 'O' in the phase diagram?
It represents the equilibrium of three phases: liquid water, ice, and vapour
What is the role of Le Chatelier's principle in the phase diagram?
It states that the melting point of ice decreases with an increase of pressure
What is the condition for a system to be nonvariant?
It has three phases and one component
What is the number of degrees of freedom in a one-phase and one-component system?
2
What do the areas AOC, AOB, and BOC represent in the phase diagram?
The conditions for stable existence of one phase
What is the normal melting point of ice at 1.0 atmosphere?
0°C
What is the term used to describe the supercooled water/vapour system?
Metastable system
What is the temperature at which the two solid polymorphic forms of sulphur, SR and SM, are in equilibrium?
95.6°C
What is the number of phases in the sulphur system represented in the phase diagram?
4
What is the term used to describe the point at which the three phases of water, ice, and water vapour coexist in equilibrium?
Triple point
What is the state of the system when it has two phases, such as water and water vapour?
Univariant
What is the process by which the supercooled water/vapour system reverts to the stable system ice/vapour?
Phase transition
What is the term used to describe the relationship between the two solid polymorphic forms of sulphur, SR and SM?
Enantiotropy
What is the degree of freedom at the equilibrium represented by the curve AC?
1
What is the significance of the point C in the phase diagram?
Both A and B are in equilibrium with the solution phase.
What is the number of phases at the point C in the phase diagram?
3
What is the effect of adding B to A on the freezing point of A?
It decreases the freezing point of A.
What type of system is represented by the phase diagram in Figure 19.5?
Simple Eutectic System
What is the degree of freedom at the point C in the phase diagram?
0
What is the phase transition that occurs when the system moves from the curve AC to the point C?
Liquid solution to solid A and solid B
What is the difference between the curves AC and BC in the phase diagram?
Curve AC represents the freezing point of A, while curve BC represents the freezing point of B.
Study Notes
Simple Eutectic Systems
- A 2-component condensed system has a phase diagram consisting of a Temperature-Concentration graph (TC graph)
- The diagram shows the freezing point curves of two components A and B, which are completely miscible in the liquid state
- The curves intersect at the eutectic point C, where both solids A and B are in equilibrium with the solution phase
Freezing Point Curves
- Curve AC: Freezing point curve of A, where the freezing point of A falls with the addition of B
- Curve BC: Freezing point curve of B, where the freezing point of B falls with the addition of A
Eutectic Point
- The eutectic point C is where the two curves AC and BC meet
- At point C, both solids A and B are in equilibrium with the solution phase
- The system has 3 phases: solid A, solid B, and the solution
- Applying the reduced phase rule equation, the degree of freedom is 0, making the system nonvariant
One-Phase Systems
- Area AOB represents the one-phase system water vapour
- Area BOC represents the one-phase system ice
- Each system has 2 degrees of freedom
- The system is bivariant
Metastable System: Supercooled Water/Vapour System
- Water can be supercooled by carefully eliminating solid particles
- The supercooled water/vapour system is metastable (unstable)
- It reverts to the stable system ice/vapour on disturbance or introduction of a crystal of ice
Polymorphic Forms of Sulphur
- Two solid polymorphic forms of sulphur: Rhombic Sulphur (SR) and Monoclinic Sulphur (SM)
- SR is stable below 95.6°C, while SM is stable above 95.6°C
- At 95.6°C, each form can be gradually transformed to the other and the two are in equilibrium
Phase Diagram of Sulphur System
- The phase diagram shows the enantiotropy of sulphur
- The diagram has four phases: two solid polymorphic forms (SR and SM), sulphur liquid (SL), and sulphur vapour (SV)
Phase Diagram of Water
- The phase diagram shows the effect of pressure on the melting point of ice
- The melting point of ice decreases with an increase in pressure
- The triple point is the point where all three phases (liquid water, ice, and vapour) are in equilibrium
Learn about the phase diagrams of two-component condensed systems, including simple eutectic systems and their temperature-concentration graphs.
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