Question

How to find the value of kp from partial pressures?

Answer 1

Answer:

Kp  is the equilibrium constant calculated from the partial pressures of a reaction equation. It is used to express the relationship between product pressures and reactant pressures. It is a unitless number, although it relates the pressures.

Introduction

In calculating Kp, the partial pressures of gases are used. The partial pressures of pure solids and liquids are not included. To use this equation, it is beneficial to have an understanding of partial pressures and mole fractions.

Partial Pressures: All of the partial pressures add up to the total pressure, as shown in the equation (Dalton's law)

Ptotal=PA+PB+...

Answer 2

Explanation:

Some 'VERY rough rules of thumb' for an equilibrium Kp value and the 'position' of the equilibrium in terms of LHS (e.g. original reactants or products of backward reaction) and the RHS (products of the forward reaction):

For: LHS  RHS

(for A + B  C + D the rules below work ok BUT once the ratios of reactants or products are not 1:1, things are not so simple)

If Kp is >> 1 the equilibrium is mainly on the RHS, maybe virtually 100% completion of the forward reaction i.e. a very large RHS yield i.e. and likely to be very thermodynamically feasible.

If Kp is approx. 1 the equilibrium is more evenly distributed between the RHS and LHS.

Kp) is << 1 the equilibrium is mainly on the LHS, maybe virtually 0% of products of the forward reaction i.e. a very low RHS yield i.e. likely to be less thermodynamically feasible.

BUT remember, Kp changes with temperature considerably changing the position of an equilibrium, AND, at constant temperature, and therefore constant K, the position of an equilibrium can change significantly depending on relative concentrations/pressures of 'reactants' and 'products'.

Finally a catalyst may speed up getting to the equilibrium but a catalyst cannot affect the position of the equilibrium constant or the value of the equilibrium constant K (Kc or Kp).