Steiner (or "Mr. Steiner" as we addressed our professors
at egalitarian Oberlin) had what seemed to me a distinctive style.
would open his lectures in the auditorium of Kettering Hall by
asking for questions, but he would never look up to see whether any
hands were raised.
one lecture. It's not a stenographic transcription I
can't write that fast but was probably written down after the
class to preserve the gist of the lesson that day.
February 6, 1966
Are there questions.
recall, last time we were discussing a reaction in which oxygen from
the air combined with glucose an aqueous solution of glucose
to give us water and some other oxidation products. And
we did this by means of certain substances that changed color as the
various parts of the reaction took place.
observing the changes in color, one was able to determine the rates
at which the reaction proceeded; and we found that these rates were
dependent upon the concentrations of the various substances in the solution.
turns out, the rate is proportional to the concentration of
methylene blue times the concentration of glucose times the
concentration of hydroxide ion; so we have this sort of relation.
The equation for the reaction is glucose plus oxygen, gaseous,
equals water plus oxidation products.
Ah. But in our expression for the rate of reaction, we
have two substances [underlines MB and OH-] that don't even appear in
the net reaction. Why not? Because they're catalysts.
aren't used up in the reaction, but they're recovered and can be used
over again. If I start out with one mole of hydroxyl ions, I
have one mole left when I get done. The hydroxyl isn't used up.
presence does make a difference.
If I have
two moles of hydroxyl ion instead of one, then the concentration of
OH- is doubled, so the rate is doubled.
If I have
half a mole, the concentration is half of the original and the rate
is only half as great.
If I don't
have any, the concentration is zero, so this product [the right half
of the rate expression] is zero, and the rate has to be zero, which
means the reaction won't take place.
doesn't mean that this reaction [indicating the second
equation, glucose plus oxygen equals water plus oxidation products]
won't take place. It's still possible to oxidize glucose by
other methods, by using a different sort of mechanism, such as is
used for oxidizing glucose in the body.
particular mechanism, the set of reactions, we've been discussing
requires the presence of hydroxyl ion and methylene blue,
also, by the way. If these two species aren't present, the
reaction won't take place.
reason is that these two species actually take part in the
reaction. They're changed. And then later on, they're
converted back into their original forms, so that the net effect is
of you, I imagine, have been taught in high school that a catalyst is
something that affects the rate of a reaction but doesn't take
part in it. I'm afraid you're going to get into trouble if you
think of catalysts merely as cheerleaders. They don't just
stand by on the sidelines encouraging a reaction. They actually
enter into the reaction. But it happens that, later on in the
reaction, they're converted into their original forms again.
catalysts are very important. If they're included in a process,
the process can't take place without them even though they
aren't mentioned in the expression for the net reaction.
That is all.