First let me say I am no chemist, so this is just In my opinion or theory until I learn better.
Much depends on how much water is involved, basically concentration, for one thing, HCl by nature has most of its portion as water, also peroxide is also high in water content, I also feel chloride is not easy to change to chlorine, also how strong the peroxide.
Chlorine gas and water form hydrochloric acid and hypochlorous acid (type of bleach)
Cl2 + H20 --> HCl + HOCl
Then hydrochlorus acid decomposes to HCl + O, hydrochloric acid and oxygen,
HOCl --> HCl + O
Halogen halides are unstable reactive substances and depending on temperature form gases
Hypochlorous acids are weak acids, and dissaociate easily.
Lets say we have HCl (approximately 80% H20 in the acid) + 3% H2O2 (approximately 97 % water).
The (HOCl) (bleach) I assume quickly breaks down in solution, giving up it’s Oxygen,
Now this solution is still is mostly hydrochloric acid and water, which some bleach has formed in solution, but quickly disassociated back to HCl and oxygen.
So here we see how an acid peroxide solution (dilute peroxide) can oxidize copper and dissolve it into HCl as copper chloride, also we see how it can momentarily try and attack gold which would quickly cement back to copper, and the bleach formed in solution is so diluted with water and is that much that basically gold is not dissolved in the reaction.
With stronger H2O2 say 30% hydrogen peroxide in a solution of HCl the bleach (HOCl) is much stronger and takes longer to disassociate, and may be forming almost as fast as it does, (my guess),
So now we have HCl and bleach in solution, and as we know this will dissolve gold, and several of the platinum group metals
Also here we have much more HOCl forming and changing back to HCL and oxygen, and depending on temperature the chlorine will gas off.
When dissolving gold we need that chlorine in solution not leaving as gas,
So heating the solution makes chlorine gas leave easier, as cold solutions hold gas easier than warm or hot solutions, which do not hold gases,
to me this a double edge sword heating makes solution dissolve gold faster but also removes the gas we need, (it can also help to remove water if heated strong enough to concentrate the acid), a cold solution will not dissolve gold very fast as chlorine is not formed in solution as easily.
many times the reactions have a lot going on inside and the chemical formula's and equations may not really explain what all is happening inside, but these do give us a way to try and explain them or figure out what maybe or might happen in a chemical reaction.
Now I am no chemist, and so this reaction, and theory of it, may not be totally true, I am just learning so until I learn different this is my guess on what happens.
Maybe a real chemist will heck out this theory and find the holes in my thoughts.
