# PCHEM Workshop 7 Notes

Updated: Dec 29, 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 breealbright@gmail.com.

**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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