Textbook Problem 4J.17

[Morgan Carrington 2H]

Assume that Δ H ° and Δ S ° are independent of temperature and use data in Appendix 2A to calculate Δ G ° for each of the following reactions at 80. ° C . Over what temperature range will each reaction be spontaneous under standard conditions? (a) B 2 O 3 (s ) + 6 HF (g ) → 2 BF 3 (g ) + 3 H 2 O (l ) (b) CaC 2 (s ) + 2 HCl (aq ) → CaCl 2 (aq ) + C 2 H 2 (g ) (c) C ( s , graphite ) → C ( s , diamond )

I thought in order to solve this problem, I would have to first use the appendix formation values to calculate the S and H of the equation, and then use the equation is equal to the - T times . However, the answer I'm getting is not right. Could someone provide a little guidance on where I could be going wrong?

[Katherine Wu 1H]

a.
deltaH=2deltaH(BF3,g)+3deltaH(H2O,l)-(deltaH(B2O3)+6deltaH(HF,g))
=2(-1137kJ/mol)+3(-285.83kJ/mol)-((-1272.8kJ/mol)+6(-271.1kJ/mol))
=-232.1kJ/mol
deltaS=2Sm(BF3,g)+3Sm(H2O,l)-(Sm(B2O3,s)+6Sm(HF,g)
=2(254.12J/K.mol)+3(69.91J/K.mol)-(53.97J/K.mol+6(173.78J/K.mol))
=-378.68J/K.mol
deltaG=-232.1J/K.mol-(353K)(-378.68J/K.mol)/(1000J/kJ)
=-98.42kJ/mol

[Morgan Carrington 2H]

Assume that Δ H ° and Δ S ° are independent of temperature and use data in Appendix 2A to calculate Δ G ° for each of the following reactions at 80. ° C . Over what temperature range will each reaction be spontaneous under standard conditions? (a) B 2 O 3 (s ) + 6 HF (g ) → 2 BF 3 (g ) + 3 H 2 O (l ) (b) CaC 2 (s ) + 2 HCl (aq ) → CaCl 2 (aq ) + C 2 H 2 (g ) (c) C ( s , graphite ) → C ( s , diamond )

I thought in order to solve this problem, I would have to first use the appendix formation values to calculate the S and H of the equation, and then use the equation is equal to the - T times . However, the answer I'm getting is not right. Could someone provide a little guidance on where I could be going wrong?

Can someone also explain how you are able to decide at what temperature the reactions are spontaneous? Especially how to understand this when it is spontaneous at all temperatures.