Saturday, 10 February 2007

Why kcal?

Careful readers may have noticed that I am slightly drawn toward theoretical chemistry. But before actually becoming a theorist I have to use my chance to complain about them.

Initially the unit of heat was defined using the specific heat of water. A calorie was the energy needed to heat up 1 gram of water by 1°C. Eventually people found out that energy and work are basically the same. The new heat unit J was equal to the work unit Nm. Many scientists accepted the new SI unit because it is easier to transform it into different units. The kcal remained only the unit of food energy.

Only the unit of food energy? No, the unit of theoretical chemistry, too. Where everyone else thinks of lunch, a theorist thinks of reactions.

I guess all a theorists really cares about is Hartrees. He transforms those into some other arbitrary unit thinking that people would like that. But isn't everybody used to kJ/mol? How much is a barrier of 8 kcal/mol? Does that mean 1 mol of my substance has to eat 2 grams of sugar to be able to react? What is the ideal gas constant in kcal/(mol K)?

On German Wikipedia I read that with 2010 it will be forbidden to use the kcal on food packaging in the EU. I sure hope that theoretical chemists will adjust faster than that.

Maybe I got it all wrong, maybe other fields are just as bad or maybe many theorists use kJ. But if not, then this had to be said.



By the way: drawing protein pictures was pretty fun. If someone liked them, I am sorry, but I am switching my topic. My biochemistry exam is over. I may get back to it eventually because there are a few mechanisms that sound really interesting. For now I'll catch up with more "pure" theoretical chemistry I wanted to talk about. Before that a little bit of organic technology, my next exam. Not really a special interest of mine. Some things are nice, though. And finally I know where chemicals come from.

6 comments:

Ψ*Ψ said...

SCORE!!!
(Mostly because I'm not nuts about biochem.) ;)

Felix said...

alright, but how can you not like biochemistry ;-)

GCT said...

Biochemistry is fun, and you get a lot of money doing research for it. One wonders though whether it would be a tremendous advantage to be really skilled at theoretical chemistry versus the strategy that most geneticists employ, which is to experiment a whole lot and then hope to discover something big, retire early, draw all of the income from a single patent.

Felix said...

I guess you need all kinds of people in research. for me it's just that I don't think I am a good experimentalist. and I like the calculations

Anonymous said...

I wonder when I'll see Hartrees on food packages, otherwise those kcal hard to understand :)

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Felix said...

yeah, that sounds good:

the new coke light with just 960 Exahartrees per bottle!