Mean Life!!! : LUSENET : UR General Chemistry : One Thread

I would just like to say that I do not think question 4 on the third exam was appropriate. It would be OK if it is not in the book (which it is not) but the fact that it is not in my lecture notes OR ANYONE ELSE'S for that matter is...disturbing. I have asked many people if they picked it up in lecture and I still get nothing. If anyone somehow heard this in one of the lectures, REPLY so we all know that it was covered. If it was not covered in lecture and is not in the book, it should not be fair game for the exam.

I have a very strong feeling that people who got the question right only fooled around with the formulas or already knew how to do mean life probs from other classes (i.e., calc). I also have a strong feeling that practically nobody got full credit on the problem, which means that NOBODY KNEW HOW TO DO IT!!!!! (Again, if you did get full credit, reply and tell us ALL when mean life was covered in lecture so I don't feel like a FOO.)

Professor Schroder, if you could tell us how many people got full credit on the problem it would make me feel more comfortable as I am having nightmares every night!!!!! NIGHTMARES!!!!! Well, OK, maybe not nightmares but it just gets to me. 20 points is very significant on the exam, and for very many people it is the difference between an A and a B. In a class where it is very hard to get an A and relatively easy to get a B, every point counts.

I am just venting now. I had to get that off my mind, as I'm SURE many people are thinking the same thing. Let me summarize: I do not think that it is appropriate to have 20% of an exam based on something that might have been BRIEFLY mentioned in lecture (or not at all) and is NOT in the book.


-- Anonymous, April 05, 2000


The term mean life was discussed in class and is covered on p. 18 of the notes. I made specifically a point of this, because the form of the time-dependent rate is then so simple and because it is often used in the literature. You can probably also guess what it means, it is the mean = average, what else!! But if you didn't get it, the consequences would not have been dire at all. I am sort of glad that this minor issue seems to be the major conceived problem with this exam, which was in fact a success for most everyone.

Good job!

-- Anonymous, April 05, 2000

Concerning the mean life again, I thought I would remind people also of my list of topics for X3, which I posted here March 29. An excerpt follows.

Hi, everyone!

The topics for the next exams are following those covered in the previous exams.


Zumdahl Ch. 15 (and course notes): Rate laws, how to determine RLs from data, method of initial rates vs integrated RLs., half-life and mean life, dating, reaction mechanisms, e.g., transition states, molecular collision approach to Arrhenius law, etc., as covered in the book.


-- Udo Schroeder (, March 29, 2000

-- Anonymous, April 10, 2000

I agree w/ you dave!!!

-- Anonymous, April 05, 2000

Mega mega dittos, Dave. I couldn't agree with you more. Is it so wrong to give a straight forward test with strictly material from the book and lectures. 20 points is a lot. Way too much to assign to a concept NO ONE HAS EVER HEARD OF. A couple of my friends and I actually spent time searching on the internet for what mean life actually is and found nothing. Apparently, it must not be a very important concept. Why don't you test us on what is important to chemistry. I didn't see any half life problems on that test. I think knowing what half life is and how to compute it is probably more important than dealing with an obscure chemical term. I'd like to head what others had to think about this latest development in the Class

-- Anonymous, April 05, 2000

Now, I could have heard this in my recitation, but I'm pretty sure it was in class--we were supposed to know mean life for the test; however, it was never covered in class. Considering it wasn't in the book, nor in my roommate's calculus book, I'm not sure exactly how we were supposed to know what it was, but I just guessed. It might have been in the web notes, but if it was I missed that page.

-- Anonymous, April 05, 2000

Well, I went to all of the last five lectures and was shocked to see Dr. Schroeder mention to me that it was covered in the class. I looked through all my notes and worse I do not have a single recollection of that topic mentioned in the class. The only way I could have missed was if I think I have been abducted by aliens and timeline was restored for me.(HAHA) But I am fairly certain that did not happen either. So I really wish for some explanation here.

-- Anonymous, April 05, 2000

As hated as this may make me, I must say that I was going through my notes after the exam and I did see "mean lifetime" mentioned. Professor Schroder mentioned the concept on March 28, 2000, towards the beginning of the lecture (I would be more than willing to photocopy my notes if people want--just e-mail me). My notes explain that for mean lifetime:

t = 1/k1, where t=time and k=rate constant

Hopefully this is the right concept/formula, and I would appreciate anyone posting the correct formula if I am wrong. It is nice and good to vent, but we might as well learn this board to learn something too eh? :) Sorry to upset/offend anyone, just saying what I have!! David Reiner

PS. I did not get full credit on the exam for this question, as I did not have the correct answer.

-- Anonymous, April 06, 2000

I too have mean life mentioned in my lecture notes from March 28th. My notes define mean life as equal to 1/K. I also saw this topic in Professor Schroeder's online lecture notes and his bb posted list of topics for the exam. Sorry all! I don't think its any less fair to make this one question worth 20 points than it was to make any other question worth 20 points.

-- Anonymous, April 06, 2000

The mean life equation was briefly mentioned during a lecture. I do have it in my notes. When I asked professor Schroder about problem #4 after the test, he told me that it was in fact in the book and that he could give me a page reference for it. He is clearly mistaken. We all know the problem was not in the book. But he did give the equation in class, so apparently for him it is fair to make it worth 20% of our test grade. It was wrong for him to do so because we never had any practice with the equation. We were never given any practice problems with it, and he certainly did not show us any examples in lecture involving the equation. Testing students on an equation that we were never given a chance to practice with is an absolute sin.

-- Anonymous, April 08, 2000

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