Contradiction between Henry's Law and Le Chatlier's Principle

[johnny_b_good]

Le Chatlier's Principle is used to determine the direction of a reaciton based upon a stress put on the system. In addition, Henry's law states that the solubility of a gas is related to the partial pressure of that gas. Therefore I present a seemingly contradictory setting:

Example for Carbonation of Water:

CO2 (g) ⇔ CO2 (aq) ---- (1)
H2O (l) + CO2 (aq) ⇔ H2CO3 (aq) ------ (2)

If I apply an external pressure on the system with an oxygen take (pure O2 (g) -- I know, very dangerous, but just a theoretical situation), then Le Chatlier's principle would argue that reaction number (1) would shift towards the right to attain the lowest possiblity energy setting. However, if we use Henry's law, then we would say that the partial pressure of CO2 (g) remains constant ... since we are adding pure O2 (g) ... and therefore, the solubility of the gas would remain constant. That is Le Chat's says concentration of CO2 (aq) increases, but Henry's says that CO2 (aq) remains constant.

Am I missing something relatively large here? thanks for the help

 

[Nessdude14]

Henry's law requires a constant temperature, and by increasing the pressure to the system, you'll cause a change in temperature, so Henry's law is invalid in this case. The reaction will behave just as Le Chatelier's principle suggests.

A gas law that would be applicable to this scenario is the ideal gas law, PV=nRT. You could determine the change of gas molecules expected from a pressure change if you also know the volume and temperature change.

 

[johnny_b_good]

Ok thanks for the help. I forgot that it dealt with constant temperature.

 

[johnny_b_good]

Well, on that note. Wouldn't increasing the partial pressure always generate a net temperature increase (no matter how small)? And thus invalidate Henry's Law?

 

[LudusRex]

There does appear to be a contradiction between Henry's Law and Le Chatelier's Principle in this scenario. However, it is important to note that these principles are based on different factors and are not always applicable in every situation.

Le Chatelier's Principle is primarily concerned with the effects of temperature, pressure, and concentration changes on a chemical equilibrium. It predicts that a system will respond to an external stress by shifting in a direction that minimizes the effect of that stress. In the case of carbonation of water, applying external pressure with pure O2 (g) would cause the equilibrium to shift towards the right, increasing the concentration of CO2 (aq) and forming more H2CO3 (aq).

On the other hand, Henry's Law is based on the relationship between the partial pressure of a gas and its solubility in a liquid. It states that the solubility of a gas in a liquid is directly proportional to the partial pressure of that gas above the liquid. In the scenario presented, adding pure O2 (g) would not affect the partial pressure of CO2 (g), therefore the solubility of CO2 (aq) would remain constant.

In this case, both principles are correct, but they are predicting different outcomes based on different factors. It is important to consider all relevant principles and factors when analyzing a chemical system. Additionally, it is possible that the effects of both principles may be observed in the scenario, but it would depend on the specific conditions and concentrations of the reactants.