Question

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

Answer 1

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.

Answer 2

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?

Answer 3

What numbers are you using. I looked up numbers and came up with -89.7 kJ. Close.

Answer 4

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

Answer 5

I mean -176.2 -(278)(o.oo588)

= -177.8

Answer 6

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

Answer 7

is this on a website?

Answer 8

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