PCHEM Workshop 4 Notes

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

WORKSHOP WITH DINELI | September 10, 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!


One mole of an ideal gas at 300 K is isothermally compressed using a constant external pressure until P = Pexternal. Because P 6= Pexternal at all but the final state, the process is irreversible. The initial volume is 25.0 L and the final volume is 10.0 L. The temperature of the surroundings is 300 K. Calculate ∆S, ∆Ssurr, and Suniv.


Calculate the change in the entropy of the system and surroundings when one mole of an ideal monatomic gas doubles its volume in: a) an isothermal reversible expansion b) an isothermal irreversible expansion into a vacuum c) an adiabatic reversible expansion d) an adiabatic irreversible expansion into a vacuum


One mole of a monatomic ideal gas, initially at 298 K and 10 L, is expanded, with the surroundings at 298 K, to a final volume of 20 L, in three ways: (a) isothermally and reversibly (b) isothermally against a constant external pressure of 0.50 atm (c) adiabatically against a constant external pressure of 0.50 atm. Calculate ∆Ssys, ∆Ssurr, ∆Suniv, ∆H and ∆T for each path.


A mole of methane is heated reversibly at atmospheric pressure until its volume doubles. The experiment is tried with two initial temperatures (a) 0 ◦C and (b) 100◦C. Calculate q, w, ∆U, ∆H and ∆Ssys for the two expansions. You can assume ideal gas behavior but because methane is not a monatomic gas you can’t use the monatomic heat capacities. For simplicity, you can assume the heat capacity is constant for each process (a) and (b). You can take this constant to be the value at the average temperature for each process (a) and (b). There is reliable data at http://webbook.nist.gov/cgi/cbook.cgi?ID=C74828&Type=JANAFG&Plot=on


Calculate ∆H and ∆S for the system and surroundings when one mole of water is vaporized at 100 ◦C. The value of ∆H¯ ◦ vap is 40.65 kJ/mol. Comment on the sign of ∆S¯◦ vap.

To anyone reviewing my notes: 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.

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