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Understanding Le Chatelier’s Principle in Chemical Equilibria

Learn how external factors such as concentration, pressure, heat, and temperature affect equilibrium reactions based on Le Chatelier’s Principle. Discover how the system shifts to counteract disturbances and maintains the equilibrium constant (K).

cedric-grimes
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Understanding Le Chatelier’s Principle in Chemical Equilibria

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  1. Le Chatelier’s principle: if a system at equilibrium is disturbed, the system will move in such a way as to counteract the disturbance.

  2. Types of disturbances: a. Concentration b. Pressure - with gases, relates to concentration c. temperature (energy)

  3. Concentration: PCl3(g) + Cl2 (g)  PCl5(g) add more Cl2? remove some PCl3? Do concentration changes affect the value of K?

  4. Pressure: 4NH3(g) + 5O2(g)  4NO(g) + 6H2O(g) Increase pressure? Decrease pressure? Do pressure changes affect the value of K? CH4(g) + 2S2(g)  CS2(g) + 2H2S(g) increase pressure? CO2(g) + C(s)  2CO(g) increase pressure?

  5. Heat: Ho = - 21.7 kcal CO(g) + 2H2(g)  CH3OH(g) CO(g) + 2H2(g)  CH3OH(g) + heat So RXN is : add Heat? What effect does a heat change have on the value of K? Remove Heat? Then in this case heat is a product. Is this endo or exo thermic?

  6. Heat: 2H2O(g)  2H2(g) + O2(g) H = 484 kJ Is heat a product or a reactant? So: 2H2O(g) + heat 2H2(g) + O2(g) H = 484 kJ add heat? remove heat?

  7. Temp. Changes: N2(g) + O2(g)  2NO(g) K@2500K = 36 x 10-4 K@2000K = 4.1 x 10-4 So is heat a product or a reactant? N2(g) + O2(g) + heat 2NO(g)

  8. External factors affecting Equilibria: Effect: Factor: value of K changes 1. Temp Change 2. Conc. change also pressure changes with gases RXN shifts to maintain value of K since K = constant: Eq mixture is the same, but Eq is reached faster. (rate is increased) 3. catalyst

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