[snorkack]

Where could the base strength of hydrogen peroxide be found?
H₂O₂2 is quoted to be weakly acidic: for the reaction
H₂O₂2 HOO^-+H⁺
the pKa is about 10^-12, with comparison to the reaction
H₂O HO^-+H⁺
whose pKw is 10^-14
But what is the equilibrium constant for the reaction
H₂O₂+H₃O⁺ H₃O₂⁺+H₂O?
I see that 100 % H₂O₂ is a solvent whose dielectric constant is close to that of water. Many polar salts possess similar solubility in hydrogen peroxide as in water, only slightly different - in either direction.
How do strong acids behave?
H₂SO₄ tends to incorporate peroxide as ligand to S.
But HCl has no such option.
So how soluble is HCl in concentrated H₂O₂?
Also how stable is H₃O₂⁺ cation towards loss of oxygen? H₂O₂ is liable to decay, but it is sluggish. Does strongly acidic reaction catalyze the decay, or not?
Note that HCl can itself stabilize hydrogen peroxide as a diluent. Hydrogen peroxide in high concentrations is liable to thermal runaway - less so at lower concentrations. Since concentrated HCl in water is under 60 % water, concentrated HCl in hydrogen peroxide might also be stabilized by the limited amount of hydrogen peroxide present...

[Enthalpy]

[...] H₂O₂ is liable to decay, but it is sluggish [...] Hydrogen peroxide in high concentrations is liable to thermal runaway [...]

In high concentration, it can and does detonate brutally. Many impurities catalyse the decomposition of H₂O₂, and in high peroxide concentration the detonation is probable.

Piranha solution suggests that acidity alone doesn't decompose reasonably concentrated H₂O₂. Some H₂O₂ remains free in the mix, and it doesn't decompose immediately.

[snorkack]

[...] H₂O₂ is liable to decay, but it is sluggish [...] Hydrogen peroxide in high concentrations is liable to thermal runaway [...]

In high concentration, it can and does detonate brutally. Many impurities catalyse the decomposition of H₂O₂, and in high peroxide concentration the detonation is probable.

Does H₂O₂ ever explode by deflagration rather than detonation?

Piranha solution suggests that acidity alone doesn't decompose reasonably concentrated H₂O₂. Some H₂O₂ remains free in the mix, and it doesn't decompose immediately.

That´s H₂O₂/H₂SO₄. What is the prevalent form of peroxide in piranha solution? H₃O₂⁺, or H₂SO₅/HSO₅^-?

[Enthalpy]

H₂O₂ can decompose slowly, or run away thermally, or make boom. I didn't check whether it deflagrates or detonates. Anyway, it's wise to avoid concentrations above 70% as far as possible.

I don't feel the prevalent form determines the stability. Even if the minor form decomposes, all will disappear.

[snorkack]

H₂O₂ can decompose slowly, or run away thermally, or make boom. I didn't check whether it deflagrates or detonates. Anyway, it's wise to avoid concentrations above 70% as far as possible.

I don't feel the prevalent form determines the stability. Even if the minor form decomposes, all will disappear.

But at a considerably slower rate. And if the equilibrium between forms is also slow, this further prevents runaway decomposition.

[Enthalpy]

No. About every reaction, even the fastest combustions and deflagrations, happens through minority species.