This might be a little bit of a basic question, but I've been trying to get my head around pressure and Le Chatelier's principle and I can't quite understand it.
Currently, my understanding of Le Chatelier's principle is that: if a change to the position of the equilibrium's position is made, the system will shift to restore the equilibrium position to be consistent with the equilibrium constant.
My current understanding of equilibrium position is essentially the ratio between concentrations of reactants and products.
So here's my problem: I understand that adding, say, more of a reactant will change the equilibrium position directly by increasing the concentration of reactants, resulting in more products being produced to restore the equilibrium position back to consistency with equilibrium constant. However, I do not understand how altering the pressure of a system has any impact on the equilibrium position? It doesn't appear to increase the concentration of either the reactants or the products? If the volume of a reaction vessel is decreased, wouldn't the concentration of the reactants and products increase proportionately?
For example, if I have 4 reactants and 2 products in a reaction vessel of 10 units cubed. Let's say the concentration of reactants is 4/10 which is 0.4, while the concentration of products is 2/10 which is 0.2. The ratio of reactants to products is 0.4:0.2 which is 2:1.
If I increased the pressure by decreasing the volume of the reaction vessel to 5 units cubed, the concentration of reactants would be 4/5 which 0.8 while the concentration of products would be 2/5 which is 0.4. The ratio of reactants to products is 0.8:0.4 which is still 2:1.
I hope I have phrased my confusion clearly. Please, if you can help explain this to me or point out a conceptual misunderstanding, I would highly appreciate it.