We have that the total enthalpy of the reaction changes with the quantity of the reactants and it is proportional to them. Also, the reverse of a reaction has the opposite enthalpy. Hence, since we need to multiply by 2, the reactants are double and thus the value of the enthalpy is 2 as big. Also, since we are using the inverse reaction, we must also invert the sign. Thus, for this reaction we must use the value H=572 kJ.
