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Le Chatelier ’ s Principle and Equilibrium

Le Chatelier ’ s Principle and Equilibrium. EQUILIBRIUM. Reversible reactions occur simultaneously in both directions . A system at equilibrium has the forward and reverse REACTIONS occurring at the same RATE

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Le Chatelier ’ s Principle and Equilibrium

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  1. Le Chatelier’s Principle and Equilibrium

  2. EQUILIBRIUM • Reversible reactions occur simultaneously in both directions. • A system at equilibrium has the forward and reverse REACTIONS occurring at the same RATE • The CONCENTRATIONS of the reactants and products are CONSTANT (not equal to each other, but unchanging)

  3. Example of a Reversible Reaction • Heat +N2O4 (g) 2NO2 (g) Colder temp Warmer temp http://genchem.chem.wisc.edu/demonstrations/Images/13equil/NO2N2O4.jpg

  4. Equilibrium Position • The relative concentrations of reactants and products at equilibrium. • At this point the concentrations don’t change unless a stress is applied to change the equilibrium. • https://www.youtube.com/watch?v=wlD_ImYQAgQ

  5. Le Châtelier’s Principle • If a stress is applied to a system in equilibrium, the system will shift to relieve the stress. • System stresses include increasing or decreasing the following: • Concentration of reactants or products • Temperature • Pressure (on gaseous systems)

  6. STRESS: CONCENTRATIONand PRESSURE • https://www.youtube.com/watch?v=7zuUV455zFs

  7. Effect of Concentration of Reactants • Adding reactant shifts the reaction toward the products. • Stress: Increasing reactants • Shift: to the right (products) • Stress: Decreasing reactants • Shift: to the left (reactants) H2O (l) + CO2(g) H2CO3(aq)

  8. Effect of Concentration of Products • Adding products shifts the reaction toward the reactants. Why? • Stress: Increasing products • Shift: to the left (reactants) • Stress: Decreasing products • Shift: to the right (replace the products) H2O (l) + CO2(g) H2CO3(aq)

  9. Effect of Pressure • Affects gases only. • For unequal number of moles of reactants and products, if pressure is increased, the equilibrium will shift to reduce the number of particles. • For equal number of moles of reactants and products, no shift occurs. 2NO2(g) N2O4(g)

  10. Ex: Effect of Pressure 2NO2(g) N2O4(g) Stress: increasing the pressure (decreases volume) Relief: decreasing the number of particles Shift: to the right (side of less molecules) Stress: decrease the pressure (increases volume) Relief: increasing the number of particles

  11. Effect of Temperature and Catalyst • https://www.youtube.com/watch?v=XhQ02egUs5Y

  12. Effect of Temperature • Increasing the temperature causes the equilibrium to shift in the direction that absorbs heat. (Endothermic)Stress: Increase in Temp • Shift: Towards the left • Decreasing temperature causes the equilibrium to shift in the direction that releases the heat (exothermic) • Stress: Decrease temperature • Shift:: Toward right SO2(g) + O2(g) 2SO3(g) + heat

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