Exam howlers
Wade Ramey
Actual answer from actual student: [sin(70)]/(50).
Anyone else have some howlers to share?
Wade
Isidore
What's '1'+'1'?
Actual student response: 2
Hahahaha--what an idiot!
Isidore
PS '11'
"Wade Ramey" <wrame...@home.remove13.com> wrote in message
news:wrameyxiii-4EB07...@news1.frmt1.sfba.home.com...
jim horsman
lim 8/x as xapproaches 0+.
the prof wrote down positive infinity. ( you have to imagine this- it looks
like a sideways 8.
exam question
lim 5/x etc
yup- the kid put a sideways 5. i fell off my chair when i was grading that.
GerardS
| Exam question:
|
| What's '1'+'1'?
|
| Actual student response: 2
|
| Hahahaha--what an idiot!
|
| Isidore
|
| PS '11'
In the computer language REXX, the answer would be: 2
Gerard S.
Doug Norris
>Hahahaha--what an idiot!
Probably, but you shouldn't be so hard on yourself. It's your first post,
after all.
Doug
G. A. Edgar
does not converge, and claimed "the Cauchy criterion is dissatisfied".
Full credit for that one.
--
Gerald A. Edgar ed...@math.ohio-state.edu
Simba Karkhanis
Problem: find 1/x - 1/sin(x) as x-> 0
Answer: undefined.
Proof: 1/x - 1/sin(x) = (sin(x) -x) / (xsin(x)) =
(sin - 1) / (x sin) _or_ (!!) (sin - 1) / sin(x)
Therefore, since there are two possible answers with x in the
denominator and you can't get rid of it,
and since x -> 0, the answer is undefined.
Ignacio Larrosa Cañestro
noticias wrameyxiii-4EB07...@news1.frmt1.sfba.home.com...
19/95 = 1&/&5=1/5
& = slashed 9
¿How did you correct that?
In other order of things, I have found frecuently
sen(4x)/sen(2x)=4x/2x= 2
and other many similar things ...
--
Saludos,
Ignacio Larrosa Cañestro
A Coruña (España)
ilar...@linuxfan.com
ICQ #94732648
Johannes H Andersen
Problem in two parts:
1a) A linear system of two equations: find x1 and x2.
1b) Another linear system of 3 equations: find x1,x2 and x3.
Solution: Student finds x1,x2 correctly from 1a), then
substitutes these values into 1b) to find x3! easy-peasy.
Johannes
Gerry Myerson
<wrameyxiii-4EB07...@news1.frmt1.sfba.home.com>, Wade
Ramey <wrame...@home.remove13.com> wrote:
=> Anyone else have some howlers to share?
Question: Are the disk and the sphere homeomorphic?
Answer: The disk is, but the sphere is not.
GM
Christian Bau
Wade Ramey <wrame...@home.remove13.com> wrote:
A howler of the opposite kind, with me at the receiving end in my first
ever maths test at university:
Problem: Prove that every compact subset of R is closed and bounded.
Answer (using proof by contradiction): Let X be a compact subset of R.
Assume X is not closed and bounded.
Prof writes: Assumption is wrong. 0 points.
David C. Ullrich
Must have been years ago... we'd need to see the _exact_ words
you used to determine whether he was right in marking it wrong.
If the exact words were "Assume X is not closed and bounded"
I'd look at what followed to decide whether you had the right
idea, and if it appeared that what you intended was a correct
proof I'd comment that "not closed and bounded" was a
very very bad way to put it, because that could mean
"not (closed and bounded)" or "(not closed) and bounded" -
in fact I think the usual operator precedence would say
it's the second. If the rest of the proof was correct, and
showed that you meant the first, I'd mark it correct but
say you should have phrased it differently, perhaps
""Assume X is neither closed nor bounded".
I doubt the previous paragraph is directly relevant because
I doubt those were your exact words. But I think a person
does need to know what the exact words were before
deciding the professor did anything howlable here.
(I know that when _I_ see an exact transcription of
something I wrote as an undergraduate I find it hard
to believe that I actually wrote what I wrote...)
Christian Bau
> On Mon, 12 Mar 2001 14:29:00 +0000, christ...@isltd.insignia.com
> (Christian Bau) wrote:
>
> >In article <wrameyxiii-4EB07...@news1.frmt1.sfba.home.com>,
> >Wade Ramey <wrame...@home.remove13.com> wrote:
> >
> >> Problem: Find the limit of [sin(7x)]/(5x) as x -> 0.
> >>
> >> Actual answer from actual student: [sin(70)]/(50).
> >>
> >> Anyone else have some howlers to share?
> >
> >A howler of the opposite kind, with me at the receiving end in my first
> >ever maths test at university:
> >
> >Problem: Prove that every compact subset of R is closed and bounded.
> >
> >Answer (using proof by contradiction): Let X be a compact subset of R.
> >Assume X is not closed and bounded.
> >
> >Prof writes: Assumption is wrong. 0 points.
>
> Must have been years ago... we'd need to see the _exact_ words
> you used to determine whether he was right in marking it wrong.
Well, it was the first line of a proof by contradiction, and after
complaining I got full points for this one :-) However, it was one of his
assistants giving the 0 points, and I guess one can make quite a few
mistakes after going through over hundred exam papers...
Also, the various math departments at my university had quite a strong
tradition to give you extra points if you turned up at the review date and
could prove that you could solve the exam problems _now_. So after every
test you would take the exam papers home and make sure that you could
solve each problem in the test to be prepared for the exam review.
William Hale
> >
> >Answer (using proof by contradiction): Let X be a compact subset of R.
> >Assume X is not closed and bounded.
> >
> >Prof writes: Assumption is wrong. 0 points.
>
> I say you should have phrased it differently, perhaps
> ""Assume X is neither closed nor bounded".
I don't think that this is the correct phrasing either. It says
that X is not closed and not bounded. It should say "Assume
X is not closed or not bounded."
I think that some logicians use the connector "nand" in this
situation instead of "nor", but I would not recommend that word.
--
Bill Hale
Christian Bau
ha...@tulane.edu (William Hale) wrote:
In the given context this is all nitpicking. If a problem "if X then A and
B" is posed, and a proof starts with "Assume that not A and B" then it is
quite obvious that this is going to be a proof by contradiction and it is
obvious that what is meant is the negation of (A and B).
Quite apart from that: A proof of A and B can be done as follows:
Part 1: Assume that (NOT A) and B. Prove by contradiction that this
assumption is wrong. This proves that A or (NOT B).
Part 2: Assume that NOT B. Prove by contradiction that this assumption
is wrong. This proves B.
Part 3: (A or (NOT B)) and (B) => A and B.
So dismissing a proof after reading "Assume that NOT A and B" without
reading any further is definitely wrong.
Oscar Lanzi III
entrance exam for the chem. engineering program:
Find the pH at room temperature of the following aqueous solutions: (a)
10^(-2) M HCl, (b) 10^(-5) M HCl, (c) 10^(-8) M HCl.
Anyone who knows basic chemistry is aware that an acidic solution can't
have a pH more than 7 at room temperature, yet I learned later from a
prof that several persons answered:
(c) pH = 8.
(The actual pH in (c) is about 7; with that little acid it's still
controlled by water's own internal ionization.)
--OL
David C. Ullrich
wrote:
>In article <3aae2e70...@nntp.sprynet.com>, ull...@math.okstate.edu wrote:
>> On Mon, 12 Mar 2001 14:29:00 +0000, christ...@isltd.insignia.com
>> >Problem: Prove that every compact subset of R is closed and bounded.
>> >
>> >Answer (using proof by contradiction): Let X be a compact subset of R.
>> >Assume X is not closed and bounded.
>> >
>> >Prof writes: Assumption is wrong. 0 points.
>>
>[cut]
>> I say you should have phrased it differently, perhaps
>> ""Assume X is neither closed nor bounded".
>
>I don't think that this is the correct phrasing either. It says
>that X is not closed and not bounded. It should say "Assume
>X is not closed or not bounded."
It appears that things I post from the office are taking infinitely
long to appear again, so although I already said this I should
say it again:
No, I don't think it was incorrect "phrasing" - that implies some
fuzziness or ambiguity. What I said was simply _wrong_-
I was thinking and typing simultaneously, but on two different
topics.
Antonio González
> Wade Ramey wrote:
>
> > Anyone else have some howlers to share?
Last year, my students (inside a problem of phisics)
had to solve the equation
(cos x)^2=1
One of them managed to obtain the answer
x=5Pi/12
Antonio
Kevin Foltinek
I have a reverse exam-howler, from my undergraduate quantum mechanics
classes.
On the final exam for the first QM class in the sequence was a
question something like "if f and g are analytic functions, prove ..."
(something about eigenvalues and operators on Hilbert spaces). It
turned out that the statement was false (in a very major way, i.e., it
was false if one of the analytic functions was nonlinear). (In fact,
looking back on it, the question didn't really make sense if that
function was nonlinear.)
During the final exam, a couple of us gave counterexamples, everyone
else proved it, and the professor retroactively removed that question
from the exam.
At the beginning of the second course in the QM sequence, a different
professor assigned the same question as homework. Of course everyone
knew by now that the statement was false, and we all gave
counterexamples. This different professor then dismissed these
counterexamples as incorrect, because they did not include complex
analytic functions; he proceeded to prove that cos(z) is not an
analytic function of z (using his own special version of the Cauchy-
Riemann equations). We were too dumbfounded to say anything. (This,
unfortunately, was merely the beginning of a rather, umm, difficult
course.)
Kevin.
Robin Chapman
>
>At the beginning of the second course in the QM sequence, a different
>professor assigned the same question as homework. Of course everyone
>knew by now that the statement was false, and we all gave
>counterexamples. This different professor then dismissed these
>counterexamples as incorrect, because they did not include complex
>analytic functions; he proceeded to prove that cos(z) is not an
>analytic function of z (using his own special version of the Cauchy-
>Riemann equations). We were too dumbfounded to say anything. (This,
>unfortunately, was merely the beginning of a rather, umm, difficult
>course.)
Well we did have a particpant here once who insisted that f(z) = z
was not an analytic function :-(
------------------------------------------------------------
Robin Chapman, www.maths.ex.ac.uk/~rjc/rjc.html
"His mind has been corrupted by colours, sounds and shapes."
The League of Gentlemen
David C. Ullrich
wrote:
>In article <3aae2e70...@nntp.sprynet.com>, ull...@math.okstate.edu wrote:
>> On Mon, 12 Mar 2001 14:29:00 +0000, christ...@isltd.insignia.com
>> >Problem: Prove that every compact subset of R is closed and bounded.
>> >
>> >Answer (using proof by contradiction): Let X be a compact subset of R.
>> >Assume X is not closed and bounded.
>> >
>> >Prof writes: Assumption is wrong. 0 points.
>>
>[cut]
>> I say you should have phrased it differently, perhaps
>> ""Assume X is neither closed nor bounded".
>
>I don't think that this is the correct phrasing either. It says
>that X is not closed and not bounded. It should say "Assume
>X is not closed or not bounded."
Aargh. It's not the wrong "phrasing", there's nothing unclear
or ambiguous about it. It's simply _wrong_. Aargh. Remind
me to read what I write. On second thought don't bother -
people have tried, it doesn't help.
Aargh.
Otoh I have to point out that you're _misquoting_ me here.
I did _not_ say "I say you should have phrased it differently".
There were _two_ aspects of this that I couldn't believe
I wrote seeing your reply just now. I couldn't believe
I'd mangled the logic, and I couldn't believe I'd said that
he should have phrased it differently - I couldn't say that,
not knowing how he _did_ phrase it... I didn't say that.
I don't think you should format _paraphrases_ to look like
quotations.
William Hale
(David C. Ullrich) wrote:
> On Tue, 13 Mar 2001 10:08:16 -0600, ha...@tulane.edu (William Hale)
> wrote:
> >In article <3aae2e70...@nntp.sprynet.com>,
ull...@math.okstate.edu wrote:
> >> On Mon, 12 Mar 2001 14:29:00 +0000, christ...@isltd.insignia.com
> >> >Problem: Prove that every compact subset of R is closed and bounded.
> >> >
> >> >Answer (using proof by contradiction): Let X be a compact subset of R.
> >> >Assume X is not closed and bounded.
> >> I say you should have phrased it differently, perhaps
> >> ""Assume X is neither closed nor bounded".
> >
> >I don't think that this is the correct phrasing either. It says
> >that X is not closed and not bounded. It should say "Assume
> >X is not closed or not bounded."
>
> Otoh I have to point out that you're _misquoting_ me here.
> I did _not_ say "I say you should have phrased it differently".
> There were _two_ aspects of this that I couldn't believe
> I wrote seeing your reply just now. I couldn't believe
> I'd mangled the logic, and I couldn't believe I'd said that
> he should have phrased it differently - I couldn't say that,
> not knowing how he _did_ phrase it... I didn't say that.
>
> I don't think you should format _paraphrases_ to look like
> quotations.
If you didn't mean to say that he should have phrased it differently,
then I say that he should have phrased it differently.
In response to my post, Christian Bau said that all this is just
nitpicking. Maybe it would have been better if he did not receive
full credit for his solution, and had a point or two deducted, so
that he would realize that what he wrote was wrong. I think that
the fact that he got full credit eventually and that you are saying
that you did not say that he should have phrased it differently
tells him that what he wrote is correct, at least to him.
My newsreader provider doesn't allow me to respond with more
quoted text than new text, so I have to do some editing and
cutting. I thought that my paraphrase of your comments was
correct. In fact, I am surprised that you disagree.
--
Bill Hale
Steven E. Landsburg
I asked "Is there a smallest positive real number. Why or why not?"
A student wrote: "There is no smallest positive real number, because
if you thought you had found the smallest positive real number, you
could divide it in half a get a smaller one."
Full credit. But he went on:
"Then you can take the result of that calculation, divide it in half
and get still a smaller one. Then you can divide in half again to get
something still smaller. Then you can do it again. This process
generates a sequence that goes on forever. It is infantile."
Steven E. Landsburg
--
Wade Ramey
Wade
kfost...@my-deja.com
<kill...@pointecom.net> writes:
>Brandon Hombs wrote:
[snip]
>> However, one student put:
>> sin(x)/cos(x) = in/co
>> How do you respond to an answer like that?!?
>> (snip)
> With the frustrated "That's not even wrong!"
You better not say that to the student! If you
do, the student will say, "So, I get full credit,
right?" I'm not sure what the correct response to
THAT would be, but then I haven't taken the program
od studies at the Institute of Applied Violence...
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kfost...@my-deja.com
<kill...@pointecom.net> writes:
>Brandon Hombs wrote:
[snip]
>> However, one student put:
>> sin(x)/cos(x) = in/co
>> How do you respond to an answer like that?!?
>> (snip)
> With the frustrated "That's not even wrong!"
You better not say that to the student! If you
do, the student will say, "So, I get full credit,
right?" I'm not sure what the correct response to
THAT would be, but then I haven't taken the program
of studies at the Institute of Applied Violence...
Christian Bau
(William Hale) wrote:
> In response to my post, Christian Bau said that all this is just
> nitpicking. Maybe it would have been better if he did not receive
> full credit for his solution, and had a point or two deducted, so
> that he would realize that what he wrote was wrong. I think that
> the fact that he got full credit eventually and that you are saying
> that you did not say that he should have phrased it differently
> tells him that what he wrote is correct, at least to him.
Once again: The problem was "Prove X". Trying to prove this by
contradiction, I wrote "Assume NOT X". That is how you start a proof by
contradiction, you state something that is wrong, show that there is a
contradiction, which proves that NOT X is wrong, which in turn proves X.
The person reading the proof saw the false statement "NOT X" (but then
every proof by contradiction starts with a false statement, that is what
proof by contradiction is about), concluded that the proof was false, and
gave zero points.
The "nitpicking" part was that the original problem was "Prove A and B"
and I wrote "Assume NOT A and B". From context it is absolutely clear what
was meant, and demanding that I put brackets around this is nitpicking.
Even if the brackets were required, you can prove (A and B) by proving
that (NOT A) and B leads to a contradiction, then proving B. However, not
continuing to read the proof IS a major howler.
Dik T. Winter
> Well we did have a particpant here once who insisted that f(z) = z
> was not an analytic function :-(
Yes. T. Leko, willing to fax pictures showing he was right to everyone
interested. At that time there was a fax number in my signature, so I
also got one.
--
dik t. winter, cwi, kruislaan 413, 1098 sj amsterdam, nederland, +31205924131
home: bovenover 215, 1025 jn amsterdam, nederland; http://www.cwi.nl/~dik/
Dave L. Renfro
[sci.math Sat, 10 Mar 2001 02:54:08 GMT]
<http://forum.swarthmore.edu/epigone/sci.math/preetalpral>
wrote
> Problem: Find the limit of [sin(7x)]/(5x) as x -> 0.
>
> Actual answer from actual student: [sin(70)]/(50).
>
> Anyone else have some howlers to share?
Once, in a "math appreciation" course, part of a test I gave
had some one-variable linear equations to solve. Most of this
course was "algebra-free" since many of the students had very
weak backgrounds in math. However, solving one-variable linear
equations was one of the topics covered and this test was
given after that topic had been covered.
Question -- Solve for x: 3x - 2 = x.
Student asks during test -- "I can solve for x on the left side,
but what do I do with the x on the right side?"
Dave L. Renfro
denis-feldmann
Dave L. Renfro <ren...@central.edu> a écrit dans le message :
myy6p9...@forum.mathforum.com...
Similar one: "Let S =1+1/4+1/16+...+1/4^n; calculate 4S and deduce the value
of S "(this was written on the blackboard)
Later, I heard a voice in the back of the room muttering to herself 'Mmm,
ok, I have calculated forty-five; what do I do now"?
It took me a few minutes to understand :-)
>
> Dave L. Renfro
Brandon Hombs
refresher course before they could proceed to calculus. On one of the
exams the students were asked what sin(x)/cos(x) equaled. Obviously the
professor expected, tan(x). However, one student put:
sin(x)/cos(x) = in/co
How do you respond to an answer like that?!?
Kevin Buhr
>
> My newsreader provider doesn't allow me to respond with more
> quoted text than new text, so I have to do some editing and
> cutting. I thought that my paraphrase of your comments was
> correct.
>
Whoops! I guess you didn't say that, but I was just paraphrasing. ;)
Seriously. Please don't format your paraphrases to look like direct
quotations. It is very misleading, very frustrating, and can (in
other circumstances) cause a lot of grief for the person you are
misquoting. (People lose jobs for less.)
Editing and paraphrasing quoted text is an excellent idea, but it
doesn't have to look like a direct quotation. I do this:
In sci.math, Foo <b...@fuu.com> writes:
>
> I remember, back in 1932... or was it 1935? Nope, it was January
> 1934. I remember because my grandfather said to me, "Fooster, the
[ . . . 418 lines of boring drivel deleted . . . ]
> and that's why we named the dog Stinky.
Foo, what does this have to do with FLT?
or this:
In alt.religion.cats.cats.cats, Joe <man...@world.com> writes:
>
[ essentially, there's more than one way to skin a cat ]
Hey, pal! Skinning cats is wrong.
The combination of *not* using the "> " prefix and putting my own
words in square brackets allows me to comment on or paraphrase what
was said without anyone mistaking it for a direct quotation.
Kevin <bu...@stat.wisc.edu>
Michael Hutchings
and B are disjoint. The student first proved that A is disjoint, then
proved that B is disjoint, then concluded that A and B are disjoint.
Kristin Hein
labs answer the following on the quiz:
Q:"find the limit as x approaches 3 of 6+3pi"
A: 6+3(3) =12
they substituted 3 in for pi, not knowing it was a constant.
Lynn Killingbeck
>
> As a freshmem in college some of my friends had to take a trigonometry
> refresher course before they could proceed to calculus. On one of the
> exams the students were asked what sin(x)/cos(x) equaled. Obviously the
> professor expected, tan(x). However, one student put:
> sin(x)/cos(x) = in/co
>
> How do you respond to an answer like that?!?
>
With the frustrated "That's not even wrong!"
Lynn Killingbeck
Zdislav V. Kovarik
Lynn Killingbeck <kill...@pointecom.net> wrote:
My favorite variation:
sin x
----- = six
n
In a first year linear algebra course for "applied" programs,
one of the questions (on linear combinations) was to determine
the ratio of mixing two solutions of sulphuric acid to obtain
an intermediate concentration. One student protested that this
was a chemistry question, and his program was economics.
ZVK(Slavek)
David C. Ullrich
wrote:
I didn't say I disagree!
Look. What I said (right up to the point where I said
something stupid) was this:
"Must have been years ago... we'd need to see the _exact_ words
you used to determine whether he was right in marking it wrong.
If the exact words were "Assume X is not closed and bounded"
I'd look at what followed to decide whether you had the right
idea, and if it appeared that what you intended was a correct
proof I'd comment that "not closed and bounded" was a
very very bad way to put it, because that could mean
"not (closed and bounded)" or "(not closed) and bounded" -
in fact I think the usual operator precedence would say
it's the second. If the rest of the proof was correct, and
showed that you meant the first, I'd mark it correct but
say you should have phrased it differently,"
I state quite clearly that I don't know exactly what he
wrote and that I feel I'd need to know _exactly_
what he wrote before saying anything definite.
Then I say some things, _all_ of the form "_If_...."
If you think that those two paragraphs amount to
me saying that I _do_ think he should have
phrased it differently I give up - I don't see how
I could been more clear.
>--
>Bill Hale
Christian Bau
> In article <3AB13C...@pointecom.net>, Lynn Killingbeck
> <kill...@pointecom.net> writes:
> >Brandon Hombs wrote:
> [snip]
> >> However, one student put:
>
> >> sin(x)/cos(x) = in/co
>
> >> How do you respond to an answer like that?!?
>
> >> (snip)
>
> > With the frustrated "That's not even wrong!"
>
> You better not say that to the student! If you
> do, the student will say, "So, I get full credit,
> right?" I'm not sure what the correct response to
> THAT would be, but then I haven't taken the program
> of studies at the Institute of Applied Violence...
Maybe you should say "That's so bad, it isn't even wrong!"
Russell Easterly
something like "give the formula of a cyclic
compound where nitrogen has a triple bond".
I hadn't read the chapter where I'm sure the
author described just such a compound.
Instead, I tried to design such a compound.
I came up with a simple nitrogen ring design.
The TA took one look at it and said that the
bond angles were all wrong and such a
compound couldn't exist. Of course he
marked my answer wrong.
About two years later I read that someone
synthesized the compound I had come up with.
As the TA predicted, it was extremely unstable.
Nowadays, I think its used in airbags.
Russell
- Zeno was right. Motion is impossible.
Bill Taylor
|> compound where nitrogen has a triple bond".
|> such a compound couldn't exist.
|> As the TA predicted, it was extremely unstable.
This reminds me of an old chemical query that's long bothered me.
I'm sure it's chemically ultra-naive. But anyway...
As triple bonds are so unstable generally, and nitrogen ones in particular,
then how come N_2 is so incredibly stable and inert, when IT has one?
-------------------------------------------------------------------------------
Bill Taylor W.Ta...@math.canterbury.ac.nz
-------------------------------------------------------------------------------
There are essentially two forms of science - physics and stamp-collecting.
-------------------------------------------------------------------------------
Russell Easterly
"Bill Taylor" <mat...@math.canterbury.ac.nz> wrote in message
news:996sbn$jt2$4...@cantuc.canterbury.ac.nz...
> "Russell Easterly" <logi...@home.com> writes:
>
> |> compound where nitrogen has a triple bond".
>
> |> such a compound couldn't exist.
>
> |> As the TA predicted, it was extremely unstable.
>
>
> This reminds me of an old chemical query that's long bothered me.
> I'm sure it's chemically ultra-naive. But anyway...
>
>
> As triple bonds are so unstable generally, and nitrogen ones in
particular,
> then how come N_2 is so incredibly stable and inert, when IT has one?
I was hoping someone who actually knows would answer.
If I remember right (btw I have a terrible memory)
molecular nitrogen "resonates" between a double
and triple bond. This resonate state is more stable
than either a triple or double bond. Good thing, too,
since a nitrogen double bond isn't very stable.
Nitrogen has an amazing number of oxidation states.
It can accept up to 3 electrons or donate up to 5.
I looked nitrogen up on the internet and found some
interesting factoids. Nitrogen makes up 78% of
our atmosphere but represents less than 3% of
the Martian atmosphere. If there is life on Mars,
it better not depend on nitrogen.
Russell
- 2 many 2 count
Tapio
"Russell Easterly" <logi...@home.com> wrote in message
news:HK7u6.599640$U46.18...@news1.sttls1.wa.home.com...
307-308:
"... nitrogen forms the multiple-bonded diatomic molecule :N(triple-bond)N:
, with an extremely short internuclear distance (1.094 Å) and very high bond
strenght. Nitrogen also forms triple bonds to other elements including
carbon (H_3CCN), sulfur (F_3SN) and some transition metals (O_3OsN-)."
Ref: W.L.Jolly "The Chemistry of the Non-Metals", p 72:
"The atoms are held together in the molecule by a triple bond. The
dissocation energy 225.1 kcal/mole, is one of the highest known and accounts
for the fact that, at ordinary temperatures, nitrogen is almost as inert as
noble gas."
Exam Q#3: " What is courage?"
A student wrote laconically: "This." and got full points.
Another student did not answer to the question, but claimed to have full
points, because he had courage to pass question without answer.
Tapio
Russell Easterly
"Tapio" <hurm...@dlc.fi> wrote in message news:99cg10$q4n$1...@tron.sci.fi...
>
> "Russell Easterly" <logi...@home.com> wrote in message
> news:HK7u6.599640$U46.18...@news1.sttls1.wa.home.com...
> >
> > "Bill Taylor" <mat...@math.canterbury.ac.nz> wrote in message
> > news:996sbn$jt2$4...@cantuc.canterbury.ac.nz...
> > > "Russell Easterly" <logi...@home.com> writes:
> > >
> > > |> compound where nitrogen has a triple bond".
> > >
> > > |> such a compound couldn't exist.
> > >
> > > |> As the TA predicted, it was extremely unstable.
> > >
> > >
> > > This reminds me of an old chemical query that's long bothered me.
> > > I'm sure it's chemically ultra-naive. But anyway...
> > >
> > >
> > > As triple bonds are so unstable generally, and nitrogen ones in
> > particular,
> > > then how come N_2 is so incredibly stable and inert, when IT has one?
> Ref: W.L.Jolly "The Chemistry of the Non-Metals", p 72:
> "The atoms are held together in the molecule by a triple bond. The
> dissocation energy 225.1 kcal/mole, is one of the highest known and
accounts
> for the fact that, at ordinary temperatures, nitrogen is almost as inert
as
> noble gas."
>
I know this is off topic, but I can't resist the temptation
to display my ignorance.
The nitrogen triple bond is extremely stable (see above).
A lot of energy is released when such a strong bond is broken.
This is why high explosives often have nitrogen triple bonds.
The trick, of course, is how to break such a strong bond easily.
Chemical bonds have a prefered angle with respect to
the other bonds. The bond becomes weaker the further away
from this angle the bond actually is.
In most high explosives the triple nitrogen bond
is strained almost to the breaking point.
So it only takes a small amount of energy to break
the triple bond in these compounds, but a large
amount of energy is released when the bond breaks.
Bill Taylor
|> I know this is off topic, but I can't resist the temptation
|> to display my ignorance.
Me too! And what's the use of asking on sci.chem - they'd just reply with
endless quantities of figures... which we know isn't REAL science at all! ;-)
|> The nitrogen triple bond is extremely stable (see above).
|> A lot of energy is released when such a strong bond is broken.
Surely that's not right? Being explosive means being able to release a lot
of energy, which means being UNstable, (to some extent). The converse
is certainly true... if a compound is in the lowest energy state for
its various ingredients, it CANT explode, or do anything without help
(e.g. some ambient oxygen), coz there's nowhere else to go - it's in
an energy pit, and is thus totally stable - as stable as can be.
Now it may be there are very stable explosives that need a lot of energy
to release a lot more - they're in a deep energy well whose base is still
a lot higher than the surrounding chemical-mix plain. But that doesn't
seem to be the case with N_2.
|> In most high explosives the triple nitrogen bond
|> is strained almost to the breaking point.
|> So it only takes a small amount of energy to break
|> the triple bond in these compounds, but a large
|> amount of energy is released when the bond breaks.
Yep, that's the usual case. Both unstable *and* highly explosive.
But some are highly explosive but still quite stable (e.g. solid rocket fuel).
But none of this helps explain why N_2 with its triple bond is both
very stable and very non-explosive, indeed non-reactive; when triple bonds,
especially N ones, are usually very unstable AND energy-full.
N_2 breaks the mould here on both counts. Why?
-----------------------------------------------------------------------------
Bill Taylor W.Ta...@math.canterbury.ac.nz
-----------------------------------------------------------------------------
kill shoot hit bomb phosgene sarin tnt c-4
anarchy rifle machine gun pistol drugs KKK
cocaine heroin pot marijuana hemp nuke
smuggle sex pervert child porn hit man
Panthers revolution assassination -- and a happy day to all you
guys and gals in the S.I.S!
-------------------------------------------------------------------------------
Tapio
> "Russell Easterly" <logi...@home.com> writes:
>
> |> I know this is off topic, but I can't resist the temptation
> |> to display my ignorance.
>
(cut)
> But none of this helps explain why N_2 with its triple bond is both
> very stable and very non-explosive, indeed non-reactive; when triple
bonds,
> especially N ones, are usually very unstable AND energy-full.
>
> N_2 breaks the mould here on both counts. Why?
Hardly cannot resist.. ;-) ....
and think about the heat of the formation is zero for N-2 (and for any other
pure element. Some are more explosive - for instance H_2).
Tapio
> Bill Taylor W.Ta...@math.canterbury.ac.nz
John R Ramsden
>
> > The nitrogen triple bond is extremely stable (see above).
> > A lot of energy is released when such a strong bond is broken.
>
> Surely that's not right? Being explosive means being able to release
> a lot of energy, which means being UNstable, (to some extent).
Surely the whole idea of an explosive is to release a lot of power,
i.e. energy or, equivalently, work done in a given time.
Weight for weight, I believe petrol ("gas" for US readers) releases
far more energy than Nitro Glycerene; but the point is it can't
do so nearly as fast.
P.S. One of the most powerful commercially available high-explosives
is Semtex, whose active ingredient is PETN, or pentanyl tetranitrate,
whose name suggests to me a four-fold nitrogen bond.
(sci.chem added - do your worst guys!)
Cheers
---------------------------------------------------------------------------
John R Ramsden (j...@redmink.demon.co.uk)
---------------------------------------------------------------------------
The new is in the old concealed, the old is in the new revealed.
St Augustine.
---------------------------------------------------------------------------
Uncle Al
>
> mat...@math.canterbury.ac.nz (Bill Taylor) wrote:
> >
> > > The nitrogen triple bond is extremely stable (see above).
> > > A lot of energy is released when such a strong bond is broken.
> >
> > Surely that's not right? Being explosive means being able to release
> > a lot of energy, which means being UNstable, (to some extent).
>
> Surely the whole idea of an explosive is to release a lot of power,
> i.e. energy or, equivalently, work done in a given time.
>
> Weight for weight, I believe petrol ("gas" for US readers) releases
> far more energy than Nitro Glycerene; but the point is it can't
> do so nearly as fast.
>
> P.S. One of the most powerful commercially available high-explosives
> is Semtex, whose active ingredient is PETN, or pentanyl tetranitrate,
> whose name suggests to me a four-fold nitrogen bond.
>
> (sci.chem added - do your worst guys!)
Gasolne doesn't include its own oxidizer. If you disperse the vapor
in air and then ignite it - fuel-air munitions - you can get the
largest explosions short of nuclear. The renowned shock sensitivity
of nitroglycerin disappears if you degas it - bubbles make a big
difference. Hollow glass microballoons are big business in
reproducibly sensitizing explosives.
PETN is a nitric acid tetraester. If you want nitrogen
polyconnectivity, look at the wurtzane-structured explosives.
--
Uncle Al
http://www.mazepath.com/uncleal/
http://www.ultra.net.au/~wisby/uncleal/
(Toxic URLs! Unsafe for children and most mammals)
"Quis custodiet ipsos custodes?" The Net!
James Hunter
John R Ramsden wrote:
> mat...@math.canterbury.ac.nz (Bill Taylor) wrote:
> >
> > > The nitrogen triple bond is extremely stable (see above).
> > > A lot of energy is released when such a strong bond is broken.
> >
> > Surely that's not right? Being explosive means being able to release
> > a lot of energy, which means being UNstable, (to some extent).
>
> Surely the whole idea of an explosive is to release a lot of power,
> i.e. energy or, equivalently, work done in a given time.
>
> Weight for weight, I believe petrol ("gas" for US readers) releases
> far more energy than Nitro Glycerene; but the point is it can't
> do so nearly as fast.
The "fastness" doesn't have anything to do with stability with explosives.
H-bombs are superstable independent of how unstable quantum-tritium
people are.
Lloyd R. Parker
: mat...@math.canterbury.ac.nz (Bill Taylor) wrote:
: >
: > > The nitrogen triple bond is extremely stable (see above).
: > > A lot of energy is released when such a strong bond is broken.
: >
: > Surely that's not right? Being explosive means being able to release
: > a lot of energy, which means being UNstable, (to some extent).
Of course, NO energy is released when a bond is broken. Bond breaking
requires energy. Energy is released when a bond is formed.
Dr. Artem Evdokimov
> is Semtex, whose active ingredient is PETN, or pentanyl tetranitrate,
> whose name suggests to me a four-fold nitrogen bond.
Kiddies, PETN is pentaerytrol tetranitrate, also known as C(CH2ONO2)4. I
am not sure about what four-fold nitrogen bond is supposed to mean, but
PETN and NG belong to the same group of explosive substances, namely the
nitric acid esters.
I once made C(CH2N3)4 which was a jolly good explosive and a whole lot
of fun to have. Don't make it at home.
A.
--
|Dr. Artem Evdokimov Protein Engineering |
| NCI-Frederick Tel. (301)846-5401 |
| FAX (301)846-7148 |
| eudo...@mail.ncifcrf.gov |
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