[makbook]

I'm in my junior year of high school and we've just been taught Le Chatelier's Principle. It's been introduced to me as something that we just need to memorize, but I was wondering if there was any reasoning behind it.

According to Le Chatelier's Principle, changing the amount of a particular substance in a dynamic equilibrium will favor the reaction that reduces that change i.e. in the reversible reaction between hydrogen and nitrogen to produce ammonia, increasing the amount of nitrogen will increase the rate of reaction between hydrogen and nitrogen. This particular part of the principle, I've found, is supported by kinetic theory -- increase in concentration of the nitrogen means increased number of collisions between particles and thus more successful reactions.

Are the other parts (temperature and pressure) of the Le Chatelier's Principle supported by kinetic or collision theory? I've done a bit of research on my own but they mostly come with mathematical proofs that are a bit too hard for me to understand.

Thanks in advance!

- Edward

[curiouscat]

Exo / endo therm affects ΔH which then changes ΔG which affects Keq. T enters ΔG equation.

Pressure enters via activities. Keq is a ratio of activities. Ideal gas activity is its partial pressure.

[Babcock_Hall]

I usually see LeChatelier's principle used when explaining a thermodynamic, as opposed to a kinetic phenomena.  In other words, people discuss the displacement of a certain equilibrium.

[cheah10]

Consider N₂ + 3H₂  2NH₃

First, I want to ask you.
For this equation, when pressure increases, do you know the reason for why more N₂ and H₂ will be converted to NH₃ but not the other way round?
It's because there are less molecules on the right hand side of the equation compared to the left. The system will convert more N₂ + H₂ to become NH₃ to reduce the number of molecules, hence reduce the pressure and consequentially reduce the change. Do you know this?

Assume that you know this, therefore is this your question: Why does rate of reaction of N₂ + H₂ increase when the pressure applied on the system increases?

My explanation is:
As you provide more physical pressure on the system, you are actually decreasing the volume of the whole system. As the forward reaction will reduce the number of molecules, the volume of the whole system will decrease also, as less molecules occupy less space. Vice-versa for backward reaction. Therefore, when you provide physical pressure, which decreases the volume, you are actually helping the forward reaction to happen, while slowing down the backward reaction. Therefore, the rate of forward reaction increases while the rate of backward reaction decreases at the same time.