Possible explanation for the exothermic reaction during electrolysis of water?

[FlyingPanda]

Possible Exothermic Reactions?

Hi there,

I've been doing some experimentation lately, but have come to a wall in terms of ideas for a possible explanation.

In a solution of only water and 0.5Mol Potassium Carbonate Electrolyte, a high electrical charge is passed through a tungsten cathode with an inert metal anode. This in turn releases a large amount of heat.

In experimental results, it has been confirmed that the energy output in terms of heat and water lost to evaporation is greater than the energy input, at times up to 40%. This obviously indicates an exothermic reaction occurring.

What I'd like to know are possible explanations for the nature of the reaction, as well as possible methods to test/verify the reaction.

Thanks

 

[Borek]

Have you tried two inert electrodes?

 

[FlyingPanda]

Hi all,

I've been doing some experimentation with the electrolysis of water, however I can't seem to be able to get clear gaseous results?

I have two electrodes stuck into water, with a 240DC, 3A Current passing through it. I have a 0.5Molar K2CO3 solution.

When I turn on the power, especially at lower voltages (cerca. 30-50V) you can clearly see gas evolution as there are a lot of bubbles forming around the electrodes. However, I always get negative results for simple oxygen and hydrogen tests. I MAY have gotten some positive CO2 tests? (I'm not sure, my lime water is a little bit off).

Is there any reason to explain why my electrolysis is not occurring as expected?

 

[berkeman]

You might check out the links below in "Similar Threads" to see if there are any clues there (I'm of no help beyond making that suggestion, though).

 

[symbolipoint]

My best guess is that since water is a poor conductor of electric current, some electrolytes need to be dissolved in it to allow current to flow. The cathode would attract some dissociated Hydrogen ions (actually "hydronium ions") and as they concentrate near the cathode, they may react with the carbonate, and form carbonic acid, and since this may be unstable in water, carbonic acid will break into carbon dioxide and water.

H₂CO₃ ----------------> H₂O + CO₂

The Carbon Dioxide will leave the solution as bubbles of gas.

This might not be entirely correct but is the best explanation I can think of.

 

[chemaddict]

Like the other posts, I can only offer suggestions of what your problem may be.

First, I believe K2CO3 will turn your solution basic, so pay attention to the pH of the solution because your electrolysis half-reactions will be different in an acid solution from a basic solution. See http://en.wikipedia.org/wiki/Electrolysis_of_water#Equations".

Second, after you determine exactly which half-reactions are going on (or should be going on based on the pH), you should check for competing reactions based on the standard electrode potentials of other reactions (See http://en.wikipedia.org/wiki/Table_of_standard_electrode_potentials" ).

At a glance I didn't see any gaseous products that would usurp your production of H2 or O2 and you would most likely get at least one of your desired product gases. Is there any scaling/rust occurring on the electrodes?

My suggestions: make sure your tests and testing materials are working properly on a control sample.

 

[chemaddict]

I'm curious to know if you could offer more specifics as to what all is being measured? It's hard to say based on what you've told us.

Are you keeping track of the temperature of the liquid solution? Does it drop when the evaporation occurs?

If this is your https://www.physicsforums.com/showthread.php?t=463486" then are you taking into account the enthalpies of formation of each species involved?

Just let us know more specifically what all is being measured and/or assumed and we can probably help you better.

 

[FlyingPanda]

What's being measured is the input energy via. Voltmeter + Ammeter, and the output energy as temperature of the liquid solution and mass of liquid lost.

The enthalpies of formation of species are not considered and yet there still is an overall rise in energy.

Any ideas?

 

[SlapChemist]

Incidentally, Sodium Sulphate is a way better electrolyte for this experiment if you are trying to get Hydrogen and Oxygen.

Hope this helps :)