How much energy must be added to 2 mil h2o(g) to cause it to be decomposed into h2 and o2

You must use 500 J to decompose 2 mol of H₂O(g).

The equation for the decomposition of water is

2H₂O(g) ⟶ 2H₂(g) + O₂(g); = 241.82 kJ·mol⁻¹

Energy = 2 mol × (241.820 kJ/1 mol) = 500 J

Note: The answer can have only one significant figure because that is all you gave for the moles of the gas.

the potential energy of the reactants is 200j.

from the energy diagram, the energy of the product formed is 350j; this means that, this reaction is an endothermic reaction, because it absorbs energy from its environment.

what is the question here. i think you messed up.