How much energy is needed for electrolysis to produce 2.5l of hydrogen?

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    Electrolysis Energy
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Discussion Overview

The discussion revolves around the calculation of the electric energy required for electrolysis to produce 2.5 liters of hydrogen gas at standard conditions (298K and 10^5Pa). Participants explore various methods and formulas to arrive at an answer, expressing uncertainty and confusion about the calculations involved.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant attempts to calculate the energy needed by converting the volume of hydrogen to mass and then using electrolysis constants, arriving at conflicting results.
  • Another suggests considering bond dissociation energy and Coulomb's law, although they express doubt about this approach.
  • There is a mention of the energy required to break the H2 bond, quantified as 4.52 eV, but its relevance to the overall calculation is unclear.
  • A later post provides a more structured approach to the problem, referencing Avogadro's number and the charge of hydrogen atoms, but does not clarify if this method is universally accepted.
  • Several participants express confusion and a lack of consensus on the correct method to solve the problem.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correct approach to calculate the energy needed for electrolysis. Multiple competing views and methods are presented, with uncertainty expressed throughout the discussion.

Contextual Notes

Some calculations appear to depend on assumptions about efficiency and the definitions of energy requirements in electrolysis. There are unresolved mathematical steps and varying interpretations of the problem.

Who May Find This Useful

This discussion may be useful for individuals interested in electrolysis, energy calculations, or those seeking to understand the complexities involved in determining energy requirements for chemical processes.

Patrickas
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How much electric energy needs to be used, to get 2.5l of hydrogen, when T=298K, pressure 10^5Pa? Electrolysis happens at 5V, efficiency is 75%.

I am quite lost here. Not sure were to start. I tried finding the needed current by getting hydrogen to kg and then by comparing to 0.0104*10^-6kg/C (electrolysis). I get 21.6*10^3C.
Energy - E=21600*5*0.75=60.75*10^3J

Of course wrong.

Second try:
n(H)=PV/RT i get that hydrogen has 0.1mole=0.1g=100C to electrolyse it.
Then E=100*5*0.75=375J - WRONG
 
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maybe look at the Bond dissociation energy , or the coulomb energy ,
E= q1*q2/(4pi*e*r)
q1 and q2 are the charges , e=permitivity constant r is the radius between the charges .
 
cragar said:
maybe look at the Bond dissociation energy , or the coulomb energy ,
E= q1*q2/(4pi*e*r)
q1 and q2 are the charges , e=permitivity constant r is the radius between the charges .

Very much doubt it... but if you got an answer...
 
you are trying eltrolzoye water or hydrogen .
 
cragar said:
you are trying eltrolzoye water or hydrogen .

It doesn't say.
 
well this might be the wrong way to go about this but it take
4.52eV electron volts , to break the H2 bond.
 
O maybe the answer to the problem will help - 0.13MJ
 
nothing?...damnnnnnn
 
ya man i would like to help but I’m at a loss , I don’t know why other people haven’t jumped in yet .
 
  • #10
If anyone is interested how to solve it read along. :smile:

"You have 0.1 mole of hydrogen gas produced (from pV=nRT)
So far so good
Multiply by Avogadro's number to find number of hydrogen molecules
Each molecule needs 2 hydrogen atoms
Each atom had a charge = 1.6 x 10^-19 C
Multiply number of atoms by this to get total charge
Energy transfer = voltage times charge, E=VQ
With only 75% efficiency the energy actually needed is this value divided by 0.75
Plug in the numbers and you get the quoted answer."

This is a quote from the solver.
 

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