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

• johnny_b_good
In summary, Le Chatlier's Principle and Henry's Law are two principles used to determine the direction and behavior of a reaction under different stressors. In the case of carbonation of water, Le Chatlier's Principle suggests that increasing the external pressure will shift the reaction towards the right, while Henry's Law states that the solubility of a gas remains constant under constant temperature. However, in this scenario, Henry's Law is not applicable as the increase in pressure would also cause a change in temperature, making it invalid. The ideal gas law, PV=nRT, would be more suitable to predict the behavior of the reaction under pressure changes.
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

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.

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

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?

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.

## 1. How can Henry's Law and Le Chatlier's Principle be contradictory?

Henry's Law states that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid. On the other hand, Le Chatlier's Principle states that a system at equilibrium will shift in a way that counteracts any imposed changes. These two principles seem to contradict each other because Henry's Law suggests that an increase in pressure will lead to an increase in solubility, while Le Chatlier's Principle suggests that an increase in pressure will cause the system to shift in a way that decreases solubility.

## 2. Which principle is more accurate, Henry's Law or Le Chatlier's Principle?

Both Henry's Law and Le Chatlier's Principle are accurate descriptions of physical phenomena. However, they apply to different systems and cannot be directly compared. Henry's Law applies specifically to the solubility of gases in liquids, while Le Chatlier's Principle applies to all types of chemical equilibria.

## 3. Are there any situations where Henry's Law and Le Chatlier's Principle do not contradict each other?

Yes, there are situations where Henry's Law and Le Chatlier's Principle do not contradict each other. For example, Henry's Law can be applied to a system at equilibrium, as long as the equilibrium constant is not affected by changes in pressure. Additionally, Le Chatlier's Principle can be applied to the solubility of gases in liquids by considering the equilibrium of the dissolution reaction rather than the solubility itself.

## 4. How can the contradiction between Henry's Law and Le Chatlier's Principle be resolved?

The contradiction between Henry's Law and Le Chatlier's Principle can be resolved by recognizing that they apply to different systems and conditions. They do not necessarily contradict each other, but rather describe different aspects of chemical equilibria. By understanding the limitations and applications of each principle, they can be used together to better understand and predict the behavior of chemical systems.

## 5. Can Henry's Law and Le Chatlier's Principle be used together to predict the behavior of all chemical systems?

No, Henry's Law and Le Chatlier's Principle cannot be used together to predict the behavior of all chemical systems. As mentioned before, they apply to different systems and conditions and cannot be directly compared. Other factors, such as temperature and concentration, also play a role in determining the behavior of chemical systems and must be considered in addition to these principles.

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