Pressure can affect the position of equilibrium, especially in reactions involving gases with a change in the number of moles. However, it's crucial to understand that while pressure can shift the position of equilibrium, it doesn't change the value of the equilibrium constant, K. The equilibrium constant is solely a function of temperature. Changes in pressure might alter the concentrations of reactants and products at equilibrium, but the ratio of these concentrations, which is what K represents, remains unchanged for a given temperature.

A catalyst accelerates the rate of a reaction by offering an alternative reaction pathway with a reduced activation energy. However, a catalyst does not affect the thermodynamic properties of a reaction, which means it doesn't change the equilibrium position of the reaction or the value of the equilibrium constant, K. It merely helps the system achieve equilibrium more quickly. Catalysts expedite both the forward and reverse reactions equally, ensuring that while the time to reach equilibrium is shortened, the actual equilibrium composition, as denoted by K, remains unaltered.

In theoretical terms, while K can approach very large or very small values, it will never exactly be zero or infinity. A K value approaching infinity indicates that, at equilibrium, the concentration of the products is significantly higher than that of the reactants, essentially suggesting a complete conversion of reactants to products. Conversely, a K value nearing zero implies that the reactants are hardly converted into products. However, in practical situations, if a reaction has a K value so small or so large that it's beyond the instrument's detection limit, it might be considered virtually zero or infinite for all practical intents and purposes.

The equilibrium constant, K, is purely a function of temperature for a given reaction and is not influenced by the initial concentrations of reactants or products. This is because K defines the relationship between the concentrations of products and reactants at equilibrium, and not how or when that equilibrium is achieved. The initial concentrations can affect how quickly equilibrium is reached or the pathway by which the system achieves equilibrium, but they don't change the final equilibrium position itself. Think of K as the end goal or destination of the reaction, while the initial concentrations merely dictate the starting point or route taken to reach that destination.

To experimentally determine the equilibrium constant, K, one must first allow the reaction to reach equilibrium. Once equilibrium is established, the concentrations of the reactants and products are measured. These concentrations are then inserted into the equilibrium expression for the reaction to calculate K. Various methods can be employed to measure concentrations, depending on the nature of the reactants and products. For example, spectrophotometry can be used for coloured solutions, while gas chromatography might be suitable for gaseous mixtures. It's essential to ensure that the system is genuinely at equilibrium when measurements are taken, as premature or delayed measurements can lead to inaccurate K values.