Calculations Involving Kc and Kp

Kc and Kp refer to the equilibrium constants for reactions in terms of concentration (molarity) and pressure respectively.
For a general reaction, aA + bB ⇌ cC + dD, the expression for Kc is [C]^c[D]^d / [A]^a[B]^b. Note that the coefficients from the stoichiometric equation become the powers in the equilibrium expression.
To use the Kc expression to calculate concentrations, it’s necessary to establish a table showing the Initial, Change, and Equilibrium concentrations (ICE table) of the substances involved, taking into account stoicheiometry of the reaction.
If the value of Kc is much greater than one, the equilibrium lies far to the right, signifying that products are favoured. Conversely, if it’s significantly less than one, the equilibrium is towards the left, indicating reactants are favoured.
For the calculation of Kp, use the expression Kp = Kc(RT)^(Δn), where ‘R’ is the gas constant (you can use the ideal gas law value), ‘T’ is the temperature in Kelvin, and Δn is the change in moles of gas (calculated as moles of gaseous products - moles of gaseous reactants)
Unlike Kc, Kp only includes gases in its expression. Hence, ensure to omit any solids, pure liquids, or solvents when calculating Kp.
For reactions involving gases, it’s possible to transition from concentration terms to partial pressures, using the Perfect Gas Law, PV = nRT.
Ensure the correct usage of units, especially while switching between Kc and Kp, or while using the gas law.
Understanding Le Chatelier’s Principle is paramount. It states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change.
Make sure to practise solving problems to grasp firm understanding of calculations, including the ones involving temperature change, as this affects the equilibrium constant.
Remember to use the square brackets [] to signify molar concentration in solutions, and brackets () for partial pressure in gases.
The equilibrium constant, be it Kc or Kp, is temperature-dependent. It remains constant only if temperature remains unchanged.