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Please post here any questions you might have about Test #1.
16 comments:
Anonymous
said...
Dr. B,
I know the review sheet is from an older class, so I was wondering if you can clarify that we are required to know upto Chap 5 section 1/2 for the test?
I was looking over the old quizzes, and I have a few questions about the answers for them, which may just be be the result of questions being cutoff in the online view:
Quiz 2, question 1: The answers didnt show up. Can you fix this?
Quiz 2, question 7: False? A change from 1 C to 2 C is a change of 1.8 in F from 33.8 to 35.6...
Quiz 3, question 12: again, the answers didnt show up.
Quiz 3, questions 4-7: if I understand this correctly, the only difference between boiling and evaporation is the Vapor pressure vs the total pressure. The difference between condensation and evaporation is partial pressure and vapor pressure. Which takes precedence (is more important), total pressure or partial pressure?
Quiz 4, question 1: is the reason why substances are closer to ideal at high temperatures and low pressures related to being farther from their two-phase envelope?
general question: will we be required to use interpolation on the exam, even tough in the real world, engineers can use the NIST webbook to find exact values for what they need?
quiz 7, questions 1-2: why is pressure related to internal energy and temperature related to enthalpy? Shouldnt it be the other way around, because H = U + PV?
Questioning: I tried to fix the quizzes where the answers did not show up. Let me know if this is still a problem.
Q2, #7: Doh ! FALSE.
Q3, 4-7: I am not sure I understand your question. Boiling occurs when the vapor pressure is greater than the total pressure. Evaporation occurs when the vapor pressure is greater than the partial pressure. Ask me about this in class because I do not feel like I have answered your question.
Q4, #1: Yes, it is related. But the key is that gases become more like ideal gases as their molar volume increases.
General: Yes, you will be required to interpolate on the test.
Q7, 1-2: You lost me. BOTH U and H depend on T for ALL substances. CP is DEFINED as dH/dTat constant P and CV is DEFINED as dU/dT at constant V. I don't know what is bothering you. Perhaps you should ask me this in class as well.
Do we need to write down the unit table on the cheat sheet or you will provide them with the questions? I think you would provide, right?The tables are too much....
For clapeyron equation, do we have a specific units we need to use? Is it necessary to use an absolute scale like R or K? For the HW 3 problem 5, solution used R for the temperature instead of F which was given. For dP/dT, it doesn't matter whether you use F or R because the conversion factor cancels out when you calculate dT. Finally, when you're calculating the dH(vap) with calculated dP/dT, and you multiply the temperature unit, you would get a different answer depending on the units of dP/dT which would either have R or K. So please clarify this confusion!!
Anon: No specific units are required for the Clapeyron Eqn. But, yes, you must use an ABSOLUTE temperature scale for T...Rankine or Kelvin. True, in dP*/dt ~ delta(P*)/delta(T) you do not have to use and absolute temperature scale because delta(T) in degF or degR is the same and delta(T) in degC is the same as delta(T) in Kelvin. So, NO you don't get a different answer depending on whether you use degC or degK !
Can you reload the answer solutions online? The equations you put up end up looking pixilated. For example, on HWK 1 Problem 9, the first equation you use... its subscripts can't be read. Is that n(3, air) and y (3,air)?
On the example problem 3D-1 at the end of chapter three there seem to be, in my opinion, a mistake. For delta H(12), the answer says -.00577 J/mole but I think it should be -5.77 J/mole. J = Pa meters cubed according to the conversion table on the back. Delta H(wiggle) in this case is V(wiggle) times delta P. Delta P we calculated is in Kpa and is -73.1 Kpa and when you multiply this by the V wiggle, which is in meters cubed/mole, you get unit of Kpa meters cubed / mole. This is KJ not J so you need to convert the Kpa to Pa to get it into Joules. -73.1 Kpa times the given V wiggle is -.00577 as given in the answer but this is KJ not J. Am i correct? Can anyone verify this for me and for all of us?
I'm not dr. B but i know the answer to your question. Q dot does have a unit of time and it is incorporated in Watts(W). Watts is in the units of Joules per second I believe.
16 comments:
Dr. B,
I know the review sheet is from an older class, so I was wondering if you can clarify that we are required to know upto Chap 5 section 1/2 for the test?
P:
Test 1 covers chapters 1 - 4, not ch 5.
I was looking over the old quizzes, and I have a few questions about the answers for them, which may just be be the result of questions being cutoff in the online view:
Quiz 2, question 1: The answers didnt show up. Can you fix this?
Quiz 2, question 7: False? A change from 1 C to 2 C is a change of 1.8 in F from 33.8 to 35.6...
Quiz 3, question 12: again, the answers didnt show up.
Quiz 3, questions 4-7: if I understand this correctly, the only difference between boiling and evaporation is the Vapor pressure vs the total pressure. The difference between condensation and evaporation is partial pressure and vapor pressure. Which takes precedence (is more important), total pressure or partial pressure?
Quiz 4, question 1: is the reason why substances are closer to ideal at high temperatures and low pressures related to being farther from their two-phase envelope?
general question: will we be required to use interpolation on the exam, even tough in the real world, engineers can use the NIST webbook to find exact values for what they need?
quiz 7, questions 1-2: why is pressure related to internal energy and temperature related to enthalpy? Shouldnt it be the other way around, because H = U + PV?
Questioning:
I tried to fix the quizzes where the answers did not show up. Let me know if this is still a problem.
Q2, #7: Doh ! FALSE.
Q3, 4-7:
I am not sure I understand your question.
Boiling occurs when the vapor pressure is greater than the total pressure.
Evaporation occurs when the vapor pressure is greater than the partial pressure.
Ask me about this in class because I do not feel like I have answered your question.
Q4, #1:
Yes, it is related. But the key is that gases become more like ideal gases as their molar volume increases.
General:
Yes, you will be required to interpolate on the test.
Q7, 1-2:
You lost me. BOTH U and H depend on T for ALL substances.
CP is DEFINED as dH/dTat constant P and CV is DEFINED as dU/dT at constant V.
I don't know what is bothering you. Perhaps you should ask me this in class as well.
Do we need to write down the unit table on the cheat sheet or you will provide them with the questions? I think you would provide, right?The tables are too much....
cheme:
I will give you any unit conversions you want during the test. Don't write them on your cheat sheet.
For clapeyron equation, do we have a specific units we need to use? Is it necessary to use an absolute scale like R or K? For the HW 3 problem 5, solution used R for the temperature instead of F which was given. For dP/dT, it doesn't matter whether you use F or R because the conversion factor cancels out when you calculate dT. Finally, when you're calculating the dH(vap) with calculated dP/dT, and you multiply the temperature unit, you would get a different answer depending on the units of dP/dT which would either have R or K. So please clarify this confusion!!
Anon:
No specific units are required for the Clapeyron Eqn. But, yes, you must use an ABSOLUTE temperature scale for T...Rankine or Kelvin.
True, in dP*/dt ~ delta(P*)/delta(T) you do not have to use and absolute temperature scale because delta(T) in degF or degR is the same and delta(T) in degC is the same as delta(T) in Kelvin. So, NO you don't get a different answer depending on whether you use degC or degK !
Can you reload the answer solutions online? The equations you put up end up looking pixilated. For example, on HWK 1 Problem 9, the first equation you use... its subscripts can't be read. Is that n(3, air) and y (3,air)?
On the example problem 3D-1 at the end of chapter three there seem to be, in my opinion, a mistake. For delta H(12), the answer says -.00577 J/mole but I think it should be -5.77 J/mole. J = Pa meters cubed according to the conversion table on the back. Delta H(wiggle) in this case is V(wiggle) times delta P. Delta P we calculated is in Kpa and is -73.1 Kpa and when you multiply this by the V wiggle, which is in meters cubed/mole, you get unit of Kpa meters cubed / mole. This is KJ not J so you need to convert the Kpa to Pa to get it into Joules. -73.1 Kpa times the given V wiggle is -.00577 as given in the answer but this is KJ not J. Am i correct? Can anyone verify this for me and for all of us?
Dr B,
i am confused why Q dot and q dot(through either conduction or convection) doesn't have any time component in the units though it is a rate.
sc:
I'm not dr. B but i know the answer to your question. Q dot does have a unit of time and it is incorporated in Watts(W). Watts is in the units of Joules per second I believe.
Questioning:
It is a bit late now ! Look at the solutions a little sooner and let me know if there is a problem.
There is no problem 9 on HW #1.
I think you mean HW #2.
The eqnis: n2 = n3,air = n3 y3,air.
I will make the eqns bigger in the future.
worried:
You are entirely correct ! Thank you !
sc:
Both have time units in them.
Qdot = W = J/sec.
qdot = W/m^2 = W/m^2-sec
worried:
Yes, exactly. Thank you for responding to sc's question before I could !
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