What is the standard form of enthalpy

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Phillipp



Registration date: 10/25/2007
Posts: 4

Posted: Dec 05, 2008 12:32 PM Title: Task !?

Hello,
I'm in the first semester of biology and now have to solve chemistry tasks on the internet so that I can even be admitted to the internship ...
So here's the job:
Which of the following statements is correct?

- Standard enthalpies of reaction always relate to 25 ° C, 101.3 KPa and the elements in their standard form
In thermochemical reaction equations, fractions may also appear as coefficients
-The enthalpy of reaction results from the sum of the enthalpies of the products plus the sum of the enthalpies of the educts
-If you put the enthalpy of reaction on the side of the educts, you have to reverse the sign
-The most stable form of carbon under standard conditions is diamond

So I would say that the first, second and fifth are correct ... I don't understand the third and fourth at first, but it sounds kind of wrong.
Could someone help me with that?
Greetings, Phillipp
litterman



Registration date: 09/22/2004
Posts: 2607
Place of residence: Marburg
Posted: Dec 08, 2008 11:17 PM Subject:

So in principle, of course, the admonition that you should also deal with it a little more as a biologist, otherwise you will get into the internship, but you will not pass the same

many of the tasks can be solved with wikipedia
first task see for example
http://de.wikipedia.org/wiki/Standardreaktionsenthalpie
but yes 1) is correct
2) In principle, fractions are always allowed ... but you usually try to avoid them ... looks nicer
3) is not entirely correct, make it clear to yourself what the educational enthalpies are (I miss the word education a bit ... that is what it should be about) and where you have to put in energy and where you get it out of a reaction, then it comes Solution by itself ...
4) if you have understood the principle behind it, the solution will come by itself ..
5) is a bit of a bad question ... so I'll spare you the research, experience has shown that diamond is extremely stable and durable, but it is still not the most thermodynamically stable form of carbon (here again the question is a bit ambiguous, you don't say whether it is mean mechanical stability or thermodynamic stability, but according to the previous questions the latter is more likely), diamond transforms at ~ 1500 ° C in the absence of air (otherwise it would burn) into the most stable modification: graphite.