CH302
Worksheet 1 Answer Key
for Physical Equilbria Problems from Lectures 1 through 3
For Questions 14, use the Phase diagram below.
1. What is a good general definition of the term triple point? How many triple points are found int he
phase diagram for quartz shown above?
A triple point is any point at which three distinct phases of a given species are in equilibrium. In
terms of a phase diagram, a triple point is any point at which 3 phase boundaries intersect. There are 3
in the figure above.
2. How many phase boundaries are there in the phase diagram for quartz shown above? (Hint: two of
them are found on the same line.)
There are
9
phase boundaries. The line separating Coesite from
α
Quartz and
β
Quartz is two phase
boundaries.
3. Starting at 0.1 GPa and 200 °C and isobarically raising the temperature to 2000 °C, how many phase
transitions would occur? What would the final phase be?
There would be 4 phase transitions and the final phase would be Silica Melt.
4. What is a critical point? How many are shown in the phase diagram above?
A critical point is a point temperature beyond which the species is a supercritical fluid, regardless of
the applied pressure. There are none in the diagram above.
5. Write as many assumptions involved in the derivation of the ClausiusClapeyron equation as you can.
We assume that
Δ
S
vap
is a constant, which itself assumes the gas phase acts as an ideal gas.
We assume that
Δ
H
vap
has a value unaffected by temperature or pressure.
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 Spring '11
 Cathy
 Thermodynamics, Triple point, Phase transition

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