3 Changing conditions on Kc and Kp

Effect of changing conditions on value of Kc or Kp Effect of Temperature on position of equilibrium and Kc Both the position of equilibrium and the value of Kc or Kp will change it temperature is altered N2 (g) + 3H2 (g ) 2 NH3 (g) In this equilibrium which is exothermic in the forward direction If temperature is increased the reaction will shift to oppose the change and move in the backwards endothermic direction. The position of equilibrium shifts left. The value of Kc gets smaller as there are fewer products. Catalysts have no effect on the value of Kc or Kp or the position of equilibrium as they speed up both forward and backward rates by the same amount. Effect of catalysts on position of equilibrium and Kc and Kp Increasing pressure does not change Kp. The increased pressure increases the pressure terms on bottom of Kp expression more than the top. The system is now no longer in equilibrium so the equilibrium shifts to the right increasing mole fractions of products and decreases the mole fractions of reactants. The top of Kp expression therefore increases and the bottom decreases until the original value of Kp is restored Effect of Pressure on position of equilibrium and Kp The position of equilibrium will change it pressure is altered but the value of Kp stays constant as Kp only varies with temperature p 2 NH3 p N2 p 3 H2 Kp= x 2 NH3 . P2 x N2 .P x 3 H2 .P3 Kp= x 2 NH3 . P2 x N2 x 3 H2 . P4 Kp= Where P is total pressure and x mole fraction Increasing pressure does not change Kc. The increased pressure increases concentration terms on bottom of Kc expression more than the top. The system is now no longer in equilibrium so the equilibrium shifts to the right increasing concentrations of products and decreases the concentrations of reactants. The top of Kc expression therefore increases and the bottom decreases until the original value of Kc is restored Effect of Pressure on position of equilibrium and Kc The position of equilibrium will change it pressure is altered but the value of Kc stays constant as Kc only varies with temperature N2 (g) + 3H2 (g ) 2 NH3 (g) In this equilibrium which has fewer moles of gas on the product side If pressure is increased the reaction will shift to oppose the change and move in the forward direction to the side with fewer moles of gas. The position of equilibrium shifts right. The value of Kc stays the same though as only temperature changes the value of Kc. [NH3 (g)] 2 [N2 (g) ] [H2 (g)]3. The larger the Kc the greater the amount of products. If Kc is small we say the equilibrium favours the reactants Kc and Kp only change with temperature. It does not change if pressure or concentration is altered. A catalyst also has no effect on Kc or Kp. Effect of Concentration on position of equilibrium and Kc H2 (g) +Cl2 (g) 2HCl (g) Increasing concentration of H2 would move equilibrium to the right lowering concentration of H2 and Cl2 and increasing concentration of HCl. The new concentrations would restore the equilibrium to the same value of Kc Changing concentration would shift the position of equilibrium but the value of Kc would not change.