to make 250.0L of hydrogen gas: how many moles of water would need to react and how many moles of oxygen would be produced?

To find the molar enthalpy change follow these steps:

1) find the amount of heat released in this experiment, that is Q=mcT, where m is the mass or volume of solution used, T is the rise/drop in temperature and C is the specific heat capacity of water which is 4.18

Q= 500 × 4.18 ×(70-11)= 123310 J

2) divide this value by 1000 to convert it into kJ

123310÷1000=123.31

3) divide the value of energy released by number of moles , that is, mass/Mr

number of moles of Nitrogen = 20 ÷(14+14)                                                    = 5/7 moles molar enthalpy change= 123.31÷5/7                                         = 172.634 mol/kJ