chemistry
posted by Sarah on .
When water freezes, the phase change that occurs is exothermic (DH = 6.02 kJ). Based on the change in enthalpy, you would expect that water would always freeze. Use the concepts of entropy and free energy to explain why this phase change is favourable only below o degrees Celsius

I would look up delta S for ice and for liquid water and use that in DG = DH TdeltsS to show that difference between 273 K and other temperatures.

Calculate the standard Gibbs free energy
NH3(g) + HCl(G) > NH4Cl
Ive tried but I keep getting a different answer
How do I get to the correc tanswer which is 91.2 kJ? 
What numbers are you using. I looked up numbers and came up with 89.7 kJ. Close.

Balanced equation
NH3(g) + HCl(G) > NH4Cl
deltaH = (1 mol)(314.4 kJ/mol)  (1 mol)(45.9 kJ/mol) plus (1 mol)(92.3 kJ/mol)
=176.2 kJ
deltas = (1 mol)(94.6)  (1 mol)(192.78) plus (1 mol)(186.90)
= 0.00588
DG = DH  TDS
=176.2 kJ / 0.00588
=29995 
I mean 176.2 (278)(o.oo588)
= 177.8 
Standard Gibbs free energy is DG_{f}^{o}.
I looked up delta Gfo and found
NH4Cl(s) = 201.5 kJ/mol
NH3(g) =16.5
HCl(g) = 95.3
Using those numbers I get =89.7. Check to see what those numbers are in your text table. I think you are calculating G when you want G^{o}_{f} 
is this on a website?

It may be but I picked these values out of a freshman college chemistry text.