H2 (g) + ½ O2 (g) ---> H2O (g), Δf H0 = -286kj mol-1
This means that when 1 mol of H2O (l), is formed , 286 kj of heat is released. This heat is absorbed by the surroundings, i.e., q rev = +286 kj mol-1 .
So ΔS = qsurr /T =286KJmol-1 /298K
=0.9597kjK-1 mol-1
= 959.7 JK-1 mol