Unchanged K, Changed Pressure

[Ayesha Aslam-Mir 3C]

I understand that changing pressure does not change the equilibrium constant, but I just wanted to think about this conceptually: decreasing the volume increases pressure, which increases the reaction rate. So when we look at chemical reactions (here we have conditions iddeal for an increased amount of collisions), altering a condition beyond the available mol for reacting alters overall concentrations?

I guess my confusion comes from if we are altering the mol of reactant by simply altering the concentrations when the reaction (chemical equation) is just based on mol and doesnt account for the conditions of the reaction.

[Pranav Kadiyala 1A]

To answer your first question

altering a condition beyond the available mol for reacting alters overall concentrations?

Concentration is moles/L. Thus, altering the volume (L) would change the concentration, without altering the number of moles. To answer the second question, we are not changing the number of moles. The concentration changes because the volume changes. This in no way impacts the chemical equation, so it stays constant.

[Megan Singer 3D]

I'm not sure I fully understand your question, but basically, decreasing the pressure changes the concentrations of the reactants and products because concentration is measured in mol/L. If the moles of the reactants and products stay the same but the volume of the container changes, the concentrations of the reactants and products will change (at least for gases). This means that if Q=K and then you change the pressure of the container by changing its volume, Q will not = K anymore (because the concentrations have changed). The moles of reactants or products will then change as the chemical reaction shifts right or left in order to move back towards equilibrium (K). Whether the forward (forming products) or reverse (forming reactants) reaction is favored depends on the number of total moles of gas there are on each side.