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PCHEM Workshop 7 Notes

Updated: Dec 30, 2019

Seventh workshop with Dineli for Physical Chemistry (CHEM 3321) with Dr. Nielsen at UT Dallas!

To anyone reviewing my notes: Please feel free to reach out if you need any clarification on anything I wrote but if I’m completely honest, I’m drowning in school, work, and life so I may or may not get back to you in a timely manner. 😓 Doing my best, here!

If you want to contact me for more information/ any clarification/ to start a study group/ need talk to someone… please comment below, DM me on Instagram, or send an email by clicking this link, the icon in the top right corner, or manually typing out

WORKSHOP WITH DINELI | October 15, 2019

Be sure to check Dineli’s page for her notes online. These are not the complete answers for the problem set. Make sure you plug and chug to get the individual answers! Also, verify any answers shown here — Dineli always stresses that we should verify the calculations from workshop!

Problem 1

Using the definition of Ka and the Debye-H¨uckel expression (Eq. 25.57, page 1036) for the mean ionic activity coefficient, calculate the pH of a 0.10 M acetic acid solution in (a) pure water (b) 0.1 M NaCl and (c) in 0.2 M MgSO4. Note: the formula for ionic strength is Eq. 25.52.

Problem 2

We can ice skate because the pressure on the ice lowers its freezing temperature creating a thin film of water under the skate blades. Calculate the freezing temperature of ice for a 70 kg person standing on ice skate blades of dimension 0.25 x 12.0 inches. Data: 1 inch = 2.54 cm; ρ(H2O(`)) = 0.997 g/cm3 ; ρ(H2O(s)) = 0.917 g/cm3 ; ∆Hfus(H2O) = 6.01 kJ/mol; g = 9.8 m/s2

Problem 3

Freeze drying (lyophilization) is a process where water contained in a sample is evaporated into the gas phase at low pressures and temperatures below the freezing temperature of water. What is the maximum pressure at which a sample can be freeze dried if the temperature is not to exceed -10.5 ◦C? Data: ∆H0 fus = 6.01 kJ/mol; ∆H0 vap = 40.65 kJ/mol; the vapor pressure of ice is 611 Pa at 273.15 K.

Problem 4

The vapor pressure of water at 20 ◦C is 17.54 torr. Using this data and ∆H0 vap = 40.65 kJ/mol for water calculate ∆G0 298 for the change H2O(`) → H2O(g)? (Hint: the form of the van’t Hoff equation is identical to the Clausius-Clapeyron equation)

Problem 5

The enthalpy of fusion of mercury is 2.292 kJ/mol and it freezes at 234.3 K under 1 atm pressure. The change in its volume is 0.517 cm3/mol upon freezing. At what temperature will the bottom of a 10 m high column of mercury (density 13.6 g/cm3 ) freeze?

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