[newb02]

I am taking a chemistry course and am struggling with thermodynamics problems.
Assuming Potassium feldspars (K feldspars) and kaolinite minerals can coexist and react.

Calculate the Delta G for the following the following reaction at a solution pH of 5.0.

K-feldspar   +   2H+   =   Kaolinite  +   4 H4SiO4°   +   2K+          K = 10-5.0


Which product (feldspar or kaolinite) will spontaneously form?  Assume (K+) = 10-3; (H4SiO4o) =10-5;  (H+) = 10-5; Temperature = 298° K.

My main question is how to find H+. I know to get H+ I have to take the antilog times (pH), but which factor in the equation is the unknown Delta G.  Thanks for the help.  I realize this could be a stupid question but I am taking a 400 level chemistry course and have not taken a chem class in a few years.

[Big-Daddy]

ΔG=ΔG°+RTln(Q)
ΔG°=-RTln(K)

(H+) = 10-5 (sic)

The feldspar and kaolinite are solid so a≈1 for them.