From owner-biophysics@net.bio.net Mon Feb 16 22:00:00 1998 Path: biosci!news.ohsu.edu!not-for-mail From: Matt Jones Newsgroups: bionet.biophysics Subject: Re: General question Date: 17 Feb 1998 22:38:47 GMT Organization: Vollum Institute Lines: 26 Distribution: world Message-ID: <6cd3hn$gg2$1@fremont.ohsu.edu> References: <6c1mmq$rnu$1@bignews.shef.ac.uk> NNTP-Posting-Host: 137.53.99.48 Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit X-Newsreader: Nuntius 2.0.4_68K X-XXDate: Tue, 17 Feb 1998 22:46:16 GMT In article <34E49CE9.2781@henri.chem.uleth.ca> Marc Roussel, roussel@henri.chem.uleth.ca writes: > Diamonds are thermodynamically unstable >relative to graphite at standard temperature and pressure which means >that their free energy is higher than that of graphite. Thus, every >diamond that has ever been dug out of the ground is slowly converting to >graphite. Maybe another way to say this is in terms of an energy diagram for the reaction: imagine a bell-shaped curve with the left "foot" higher than the right "foot", so that there is a hill in between. The height of the curve at each point represents the energy of the reaction (e.g., diamond turning to graphite), so that diamond (on the left) has a higher energy than graphite. Given an infinite time, all dimaonds will sooner or later slide across the reaction towards graphite, so diamond is less thermodynamically stable than graphite. However, before diamond can turn to graphite, it has to surmount an energy barrier (the hill). The lower the hill between the two states, the faster things can go over it, and the faster the reaction will proceed. If the hill is very high, then diamond will be kinetically stable, because only very rarely does an individual diamond crystal attain enough energy (from heat in the ground, or whatever) to climb over this energy barrier. Helpful, or more confusing? -Matt .