Calculating the Freezing Point of Mercury Under Pressure

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SUMMARY

The discussion focuses on calculating the freezing point of mercury under pressure, utilizing the enthalpy of fusion (2.292 kJ/mol) and the normal freezing point (234.3 K). The pressure exerted by a 10.0 m column of mercury, with a density of 13.6 g/cm³, was calculated using the equation p = ρgh. The derived temperature of 234.2 K raised questions regarding the expected increase in freezing point with increased pressure, highlighting the need for clarification on the slope of the melting point line.

PREREQUISITES
  • Understanding of thermodynamic concepts, specifically enthalpy of fusion.
  • Familiarity with the properties of mercury, including its density and normal freezing point.
  • Knowledge of pressure calculations using the formula p = ρgh.
  • Ability to manipulate and solve equations involving temperature and phase changes.
NEXT STEPS
  • Research the Clausius-Clapeyron equation for phase transitions.
  • Explore the effects of pressure on the melting/freezing points of various substances.
  • Investigate the thermodynamic properties of mercury in greater detail.
  • Learn about the slope of melting point lines for different materials and their implications.
USEFUL FOR

Students in chemistry or physics, particularly those studying thermodynamics, as well as professionals involved in materials science and engineering who require a deeper understanding of phase changes under varying pressure conditions.

winterwind
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Homework Statement


The enthalpy of fusion of mercury is 2.292 kJ/mol, and its normal freezing point is 234.3 K with a change in molar volume of +0.517 cm/mol on melting. At what temperature will the bottom of a column of mercury (density 13.6 g /cm3) of height 10.0 m be expected to freeze?


Homework Equations



p = \rhogh

p = p* + [(\DeltafusH)/(T*\DeltafusV)]/(T - T*)


The Attempt at a Solution



I calculated the pressure in the column of mercury using the first equation provided above. I then solved the second equation for T, plugged in the given values, with p*= 101 kPa and T* = 234.3 K (the normal pressure and boiling point).

I get an answer of 234.2 K, which doesn't make sense, since when you raise the pressure, shouldn't you get a higher temperature freezing/melting point? I would expect it changes more than 0.1 K anyways.

Am I using the correct equation?

Thanks!
 
Last edited:
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winterwind said:
I get an answer of 234.2 K, which doesn't make sense, since when you raise the pressure, shouldn't you get a higher temperature freezing/melting point?
What's the slope of the m.p. line? Positive? Or, negative?
winterwind said:
I would expect it changes more than 0.1 K anyways.
Water changes 0.01 K/atm, and has which slope?
winterwind said:
Am I using the correct equation?
Yes.
 

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