04-12-2018, 04:50 AM

http://wallace.chem.ox.ac.uk/teaching/1.3%20Thermodynamics%20II.pdf

Question 2B/C

So far i have calculated K using ∆rH, ∆rS, ∆rG* at 298k as (∆rH=-92,400JMol-1, ∆rS=-199JKMol-1, and ∆rG= -33,000JMol-1) and have got a value of K as 746.5, however I am skeptical about it as K seems quite large, when calculating K i used the formula LnK=-∆rG/RT using my values from part A of the question and the temperature as the one where equilibrium is reached (600K), I'm unsure whether is alter my value of ∆rG* to take into account the equilibrium temperature or if that is already accounted for by LnK=-∆rG*/RT, the next problem i encounter is setting up the question to answer part C, I have worked out a formula for K in terms of pressure and the molefractions as K after cancelling down and simplifying as K= (Xnh3)2/((Xn2) +(Xh2)3 + P2) and worked out the molefractions of N2 and H2 as 0.1625 and 0.4875 respectively using the molefraction given of Nh3=0.35 as a guide. However when rearranging to find the total pressure i find that the value of P is very small (0.09) so there must either be a mistake in part B in working out K (which seems most likely) or an error in my assumptions for C, can anyone please point out/guide me as to where I'm going wrong, any help would be greatly appreciated!

Question 2B/C

So far i have calculated K using ∆rH, ∆rS, ∆rG* at 298k as (∆rH=-92,400JMol-1, ∆rS=-199JKMol-1, and ∆rG= -33,000JMol-1) and have got a value of K as 746.5, however I am skeptical about it as K seems quite large, when calculating K i used the formula LnK=-∆rG/RT using my values from part A of the question and the temperature as the one where equilibrium is reached (600K), I'm unsure whether is alter my value of ∆rG* to take into account the equilibrium temperature or if that is already accounted for by LnK=-∆rG*/RT, the next problem i encounter is setting up the question to answer part C, I have worked out a formula for K in terms of pressure and the molefractions as K after cancelling down and simplifying as K= (Xnh3)2/((Xn2) +(Xh2)3 + P2) and worked out the molefractions of N2 and H2 as 0.1625 and 0.4875 respectively using the molefraction given of Nh3=0.35 as a guide. However when rearranging to find the total pressure i find that the value of P is very small (0.09) so there must either be a mistake in part B in working out K (which seems most likely) or an error in my assumptions for C, can anyone please point out/guide me as to where I'm going wrong, any help would be greatly appreciated!