To find the energy, you should follow the following rule :
Q= mass * latent heat of vaporization
Q= m * l
Q= 50g * 2260 J/g
Q= 113000 J
Answer;
The heat of vaporization of water is 2257-J/g - each grams must release 2257-J of thermal energy. When water condenses its temperature remains constant.
Q = m x Hv ===> 50-g x 2257-J/g = 112,850-J = 112.9-kJ
This question is based in mole ratios. for every mole of cl2, 2 moles of NaCl will be produced. so half of the moles of NaCl gives the moles of Cl2 required. therefore divide 0.35 by 2