Where does the energy come from which is needed for an endothermic reaction?

from the reactants
from the products
from the product / reactant solution
from the environment when no solution is involved
from the change in enthalpy

h let me think

when [oh-] is 10-5  m, and [h3o+] is 10-9  m, the poh is 5 and ph is 9. again in both cases the sum of ph and poh is 14. however, the hydrogen ion concentration is not always going to be equal to exactly 1 x 10 raised to a negative number. for example, we skipped over the value of 2.0 x 10-7.