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I have passed the PE Chemical exam this month, which marked the key milestone of my journey towards PE professionalism. The experience of preparing both FE and PE exams has also brought my understanding of chemical engineering subjects to a new level. Thanks a lot for those folks who actively...

I am preparing the Chemical PE and found these is a minor difference in calculating the isentropic work for closed versus open system in the reference book. The formula for isentropic work in closed system misses the specific heat ratio k on the numerator as compared with the formula for open...

@georgeverghese @pierreick Thank you both for the explanation. Did not expect this needs some math skills to obtain the first order derivative. The answer A makes total sense !

@georgeverghese Since K decreases when moving down the X axis, should f(theta) decrease as well so that answer is either C or D ? How to pick between C and D ? If f(theta) = Sum (y_i) - Sum (x_i), then f(theta) is always zero ? I need more hints. [dazed]

@Latexman Thank you providing the guidance. The answer is D if I am correct. At bubble point, Sum (KiZi) =1. At dew point, Sum (Zi/ki) = 1. Within the two phase means the temp is between bubble point and dew point temps. Thus, both Sum (KiZi) and Sum (Zi/Ki) is greater than 1. Do you have any...

@georgeverghese Thank you for the direction. I believe here is the reference you were referring to. With this, I am still having hard time to solve these two problems. Can you explain in details ?

I have been scratching head on these two thermodynamics questions. Can anyone shed some lights ? These two questions are all related to phase equilibrium. PE Reference:

@TiCl4, Oh. Now I got it. Forgot to consider the unreacted CH3CHO in the outlet. It makes total sense that the mean residence time for CSTR should be calculated based on Vout. For PFR, I guess the mean residence time should be somewhere between the numbers calculated based on Vin and Vout.

At 65% conversion which means 0.65 mol CH3CHO is converted, should it lead to 0.65 x 2 = 1.3 mol out for every mol in ? So if volumetric flow in not equals to volumetric flow out, how do we calculate the mean residence time ? I feel it should be somewhere between the number calculated based on...

Thank you so much for such a detailed explanation. Now I understand the logic behind the 1st question. I should have written two separate equations: one for NO only and the other for NO2 via NO as the intermediate. This way helps better understand the molar balance to solve the problem...

I am preparing for the PE Chemical practice exam and get stuck with these two questions. Please see the attached files. Does anyone have idea how to solve them ? Really appreciated if thought process can be shared.