[Rutherford]

1.Energies of H-H, Cl-Cl and H-Cl bonds are 432, 240 and 428kJ/mol. What minimal energy you have to spent to electrolise 1 mol of NaCl until all Cl₂ is made if dH of NaOH_(aq)+HCl_(aq) neutralisation is 55kJ/mol and dH of dissoluting HCl_(g) is 74kJ/mol?
I tried this way:
NaCl electrolisys
K^-:2H₂O+2e^--->2OH^-+H₂
A⁺:2Cl^--->Cl₂+2e^-
The whole process:
2H₂O+2Cl^--->2OH^-+H₂+Cl₂ dH I have to calculate. So, how to do it? I tried many different times using Hess' law but I couldn't get the right result.
Wanted to add another problem, but I will do that later.

[Vidya]

H2 + Cl2 -->2HCl  --- 1 (dH= BE(H2) +BE(Cl2 )-2BE(HCl)

NaOH +HCl-->NaCl +H2O ------ 2 dH= -55kJ/mol
reverse the above equations

so what is required that you multiply eq 2 by a factor of 2 .After that add both of the reversed equations.This will give you equation
2NaCl + 2H2O ----> H2 + Cl2 + 2NaOH
write net ionic equation-
2Cl- + 2H2O ----> H2 + Cl2 + 2OH-

[Rutherford]

dH for the 1st equation is -184kJ/mol. When I reverse it dH=184kJ/mol.
dH for the 2nd reversed and multiplied equation is 110kJ/mol.
I get 184+110=294kJ, but the answer is 221kJ. I figured then out that the HCl produced by H₂ and Cl₂ is a gass, and the HCl that reacts with NaOH is in an aquatic solution, so I have to use the dH of dissoluting HCl(g) is 74kJ/mol.
HCl_(g)-->HCl_(aq) dH=74kJ/mol
But I have to reverse and multiply this equation by 2 and I get the result 136kJ, but that isn't the right result, too.
Thanks for the answer, anyway.

[Caustikola]

Have you worked it out? Or can I be of help?

[Rutherford]

Still didn't get the right result. Your help would be most appreciated.

[Caustikola]

Enthalpy of formation of H+ and Ni2+ are their ionization energies. Hope this points you towards the solution. Pls reply if you get the ans

[Rutherford]

I don't understand how that can help me.
I wrote these equations:
1.H_2(g)+Cl_2(g)-->2HCl_(g) dH=-184kJ/mol (calculated from the bond energies)
2.H⁺_(aq)+OH^-_(aq)-->H2O_(l) dH=55kJ/mol
3.HCl(g)-->H⁺_(aq)+Cl^-_(aq) dH=74kJ/mol
The electrolysis equation is:
2Cl^-_(aq)+2H₂O_(l)-->H_2(g)+Cl_2(g)+2OH^-_(aq) dH=?
I tried to calculate dH using Hess' law but I couldn't get the right result (221kJ).
On accident, I got it when the sum of 184, 2*55, 2*74 I divided by 2. I suppose that it is divided by 2 because I am asked to calculate "the minimal energy you have to spent to electrolise 1 mol of NaCl" and in the equation I have 2Cl^-. But I couldn't get 184+2*55+2*74 from the Hess' law.

[Caustikola]

Sorry for my initial post. It was actually a mistake:(
 Here we go:
To tackle this problem, you can either go directly using the bond energies of reactants and products or go through hess's law
you decided hess
(which i believe is because you didn't have data for the electron affinity of Cl-)
I'm using your data here;
Overall reaction
2H2O+2Cl- --->H2+Cl2+2OH-
Then for hess's law
H2+Cl2--->2HCl
dH=-154
reversing this eqn;
2HCl--->H2+Cl2
dH=+184
Multiplying the 2nd eqn you gave by 2 gives
2H+ +2OH- --->2H2O
dH=-110
at this point i have to say you were a bit careless with your signs. The dH here should be negative not positive.
Inverting this equation gives
2H2O--->2H+ +2OH-
dH=-110
Multiplying the third equation by 2 and inverting gives
2H+ +2Cl- --->2HCl
dH=-148
 you can now apply hess law here.
 # this is electrolysis. Energy is evolved dH must be negative.

[Rutherford]

184-110-148=-74kJ/mol, but the answer is 221kJ. I suppose that from the Hess' law I should somehow get -442kJ/mol, then I need to divide it by 2 (because of the 2Cl^- ions and I am asked to calculate the "minimal energy you have to spent to electrolise 1 mol of NaCl") and from here I get -221kJ/mol, so the enegry that I have to spent would be 221kJ. The problem is, I can't get -442,+442,-221 nor +221kJ from the Hess' law. Something is wrong.

[Caustikola]

Although I made a mistake...after rearranging the 2nd eqn & multiplying by 2, the dH ought to be +110,
giving dH of the reaction=+184+110-148=+76
hess law can't be wrong; the answer should be wrong

[Rutherford]

Could be, I can't find a mistake when solving it with Hess' law either.