From owner-metabolic-reg@net.bio.net Thu Dec 23 22:00:00 1993 Newsgroups: bionet.metabolic-reg Path: biosci!daresbury!doc.ic.ac.uk!warwick!uknet!gdt!aber!hrs From: hrs@aber.ac.uk (Herbert Martin Sauro) Subject: Re: exothermic or endothermic? Message-ID: <1993Dec23.130115.20856@aber.ac.uk> Organization: University College of Wales, Aberystwyth References: <2fbpoo$shj@mserv1.dl.ac.uk> Distribution: bionet Date: Thu, 23 Dec 1993 13:01:15 GMT Lines: 27 In article <2fbpoo$shj@mserv1.dl.ac.uk> "" writes: >In my humble opinion, the fact that a process is driven by energy influx does >not necessarily make this process endothermic. The point is that DeltaG >(change in Gibbs Free Energy) need not have the same sign as DeltaH (change >in enthalpy). If a process has a positive DeltaG, i.e. it has to be driven to >operate, it may have positive or negative DeltaH, which gives the heat >exchange. > >Stefan=Schuster @ rz.hu-berlin.de Precisely! Having talked to a few other people about this, my feeling is that photosynthesis is most probably exothermic. The delta G must be negative (otherwise it wouldn't go of course) but delta G = delta H - T delta S and I imagine the delta S change is negative because we're changing things like co2 and water into gluose so there is much less freedom? This is the bit I'm not too happy about because I suppose one should consider what's happenning to the environment etc so even just deciding the sign of delta S is probably difficult. But if it is negative that obviously delta H must be negative for delta G to be negative, hence photosynthesis is exothermic? Humm.. Herbert Sauro .