Gampin Posted March 5, 2004 Share Posted March 5, 2004 Can I calculate dG with dH and without dS? Link to comment Share on other sites More sharing options...
chemistry Posted March 7, 2004 Share Posted March 7, 2004 In almost all cases no. Reactions contribute to a change in entropy. Link to comment Share on other sites More sharing options...
wolfson Posted March 7, 2004 Share Posted March 7, 2004 The combination of /_\H and -T/_\S must be NEGATIVE, indicating a release of total free energy. Thus: /_\G = /_\H - T/_\S Link to comment Share on other sites More sharing options...
aommaster Posted March 8, 2004 Share Posted March 8, 2004 ok, something new to me, so sorry if i look a little stupid. What is gibbs equation? Link to comment Share on other sites More sharing options...
YT2095 Posted March 8, 2004 Share Posted March 8, 2004 put quite simply is a calculation of energies used or given during a chemical reaction Link to comment Share on other sites More sharing options...
wolfson Posted March 8, 2004 Share Posted March 8, 2004 Yes predicting the Spontaneity of a Reaction. Link to comment Share on other sites More sharing options...
aommaster Posted March 8, 2004 Share Posted March 8, 2004 in which way exactly, don't u use bond energies for this? Link to comment Share on other sites More sharing options...
wolfson Posted March 8, 2004 Share Posted March 8, 2004 If Delta H were negative that would mean that the chemical system would lose energy to the surroundings and that should make the products more stable. /_\ represents the total energy exchange that takes place between the system and its environment and T/_\ represents the energy eused to take care of the intermolecular activity. Link to comment Share on other sites More sharing options...
aommaster Posted March 8, 2004 Share Posted March 8, 2004 Isn't this just a calculation for making sure whether a reacton is exothermic or endothermic? Link to comment Share on other sites More sharing options...
wolfson Posted March 8, 2004 Share Posted March 8, 2004 Pretty much, and energy consumption. Link to comment Share on other sites More sharing options...
YT2095 Posted March 8, 2004 Share Posted March 8, 2004 think Endothermic and Exothermic reactions, Gibbs is all rellated to that as well as the initial "trigger energies" for the reaction to take place, Gibbs is the "Maths Bit" Link to comment Share on other sites More sharing options...
aommaster Posted March 8, 2004 Share Posted March 8, 2004 So, it works with both, the activation energies AND the energies that are involved in the reactions? Link to comment Share on other sites More sharing options...
YT2095 Posted March 8, 2004 Share Posted March 8, 2004 yup! that`s about it sorry for repeating same info as Wolfson, he must type faster than me (not hard to do today, I`m in alot of pain with my hands) Wolfson, probably knows alot more about the maths and calc side than myself, he`s worth listening to! Link to comment Share on other sites More sharing options...
aommaster Posted March 8, 2004 Share Posted March 8, 2004 lol. Thanx alot! Link to comment Share on other sites More sharing options...
scientistsahai Posted March 9, 2004 Share Posted March 9, 2004 Yes we can useit without the use of dH. If we know the E(cell) then we can use the relation Delta G= - nFE(cell) I hope that relation can be used here Link to comment Share on other sites More sharing options...
Gampin Posted March 14, 2004 Author Share Posted March 14, 2004 thanks. hope dS wasn't given to me on the exam then. Link to comment Share on other sites More sharing options...
Gampin Posted March 24, 2004 Author Share Posted March 24, 2004 dS = C ln (T2 / T1) C = heat capacity. then, dG = dH - T dS so i got it wrong on the test. Link to comment Share on other sites More sharing options...
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