An exothermic reaction is spontaneous above 400K but non spontaneous below it. Of the deltaH for the reaction is -40.0 kcal, what are the values of deltaS and deltaG at 400K?

Answer 1

dG = dH - TdS
dG = 0 at 400; i.e., the dividing line between spontaneity and non-spontaneity.
dH = 40,000, T = 400 K, solve for dS.

Answer 2

If G=0 and I solve the equation for dS it would be
S= 0/(400 x 40,000).
Anything divided by 0 is zero. How can I get a value for dS?

Answer 3

Your algebra needs improving.
dG = 0
dG = dH-TdS
0 = dH - TdS
TdS = dH - 0
TdS = dH
dS = dH/T = ?