What is the relationship between temperature and HOCl dissociation?

[qwerty1232]

I am investigating the effects of temperature on the dissociation of hypochlorous acid (HOCl), and am largely trying to relate this back to the system's tendency towards a state of minimum free energy. However, I am struggling to put all the information together in a way that makes sense.

What I have so far:
1. Initially, HOCl is largely undissociated, because ionization is endothermic. However, some dissociates to OCl ion, due to entropy of mixing. The entropy of the products (H+ and OCl-) is potentially greater than that of the reactants, as there a more moles. As such, the energy levels are more closely spaced. However, the ground state of reactants is higher than products.

--> this last point is what I am really struggling with. I known that energy must be in in order to break bonds, but why does this increase ground state? There is a picture of what I mean here: http://www.chem1.com/acad/webtut/thermo/entropy.html

2. Increasing temp, --> increase KE of all particles in solution (this is unfavourable)
--> additional KE converted to PE to break bonds (Le Chateliers principle)
--> as temperature continues to rise, additional energy used to excite particles to higher energy levels (increasing entropy)


I'm really sorry for the novel, but have been researching this for weeks and am still grappling with the details. I would so grateful if anyone could indicate if I am on the right track, or to clarify any of these matters.

Thankyou very much.

 

[jbsteele]

Your explanation is mostly correct. The key point to understand is that increasing temperature increases the kinetic energy of particles, which can be used to break bonds. This is in accordance with Le Chatelier's principle, which states that a system will shift its equilibrium position in order to counteract the effect of an external stress on it. In this case, the external stress is the increase in temperature. This means that more HOCl molecules will dissociate into H+ and OCl- ions, leading to an increase in entropy (number of microstates). In addition, increasing temperature also excites the particles to higher energy levels, which increases entropy further. This is because at higher temperatures, the particles are able to access more microstates due to an increased number of energetic pathways available to them. As a result, the system tends to move towards a state of maximum entropy, which corresponds to a state of minimum free energy.