Activation energy?? The energy needed to start a chemical reaction is called activation energy
PH = -log([H+])
[H+] = 10^(-pH)
[H+] = 10^(-8.78) = 1.65*10^-9
[H+][OH-] = Kw
Kw = 1.0*10^-14 at 25 degrees celsius.
[OH-] = Kw/[H+] = (1.0*10^-14)/(1.65*10^-9) = 6.06*10^-6
The concentration of OH- ions is 6.1*10^-6 M.