Le Chatelier's Principle: Chemistry Concepts PDF

Le Chatelier’s Principle Le Chatelier’s Principle When a chemical system at equilibrium is disturbed by a stress, the system adjusts (shifts) to oppose the change Stresses include: Change in concentration Change in pressure (or volume) Change in temperature  Change in Concentra...

Le Chatelier’s Principle Le Chatelier’s Principle When a chemical system at equilibrium is disturbed by a stress, the system adjusts (shifts) to oppose the change Stresses include: Change in concentration Change in pressure (or volume) Change in temperature  Change in Concentration A(g) + 3B(g)  2C(g) + heat Increasing the concentration of the reactants OR Decreasing the concentration of the products Will favour the forward reaction, causing the equilibrium to shift to the RIGHT Decreasing the concentration of the reactants OR Increasing the concentration of the products Will favour the reverse reaction, causing the equilibrium to shift to the LEFT RECALL: Addition or removal of solid or liquids does not change the concentration. Therefore does not cause a shift. I.e. only applies to gases and aqueous solutions. Change in Concentration N2(g) + 3H2(g)  2NH3 Change in Pressure  volume  pressure  volume  pressure A(g) + 3B(g)  2C(g) + heat Increasing the volume of the container OR Decreasing the pressure Will cause a shift to the side with MORE gas molecules In our example, it will shift left (4 mol reactants > 2 molproducts) Decreasing the volume of the container OR Increasing the pressure Will cause a shift to the side with LESS gas molecules In our example, it will shift right (4 mol reactants > 2 molproducts)  Change in Temperature In an exothermic reaction: Increasing the temperature will cause a shift to the LEFT Decreasing the temperature will cause a shift to the RIGHT  Change in Temperature In an endothermic reaction: Increasing the temperature will cause a shift to the RIGHT Decreasing the temperature will cause a shift to the LEFT Change in Temperature Recall: Keq is temperature dependent. Therefore, changes in temperature will also affect Keq Shift right =  products,  Keq Shift left =  reactants, Keq DEMONSTRATION Variables that do NOT Affect Equilibrium Catalysts Increases reaction rate by lowering activation energy (of BOTH the forward and the reverse reactions equally) Decreases the time required to reach equilibrium but does not affect the final position of equilibrium Inert Gases Increases the pressure, which will increase reaction rate Increases the probability of successful collisions for BOTH products and reactants equally Decreases the time required to reach equilibrium but does not affect the final position of equilibrium Practice