Kinetics, Thermodynamics and Equilibrium - Revsworld

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5) Changing Equilibrium (HW: p. 32, 33) Objective: You will use Le Chatelier’s Principle to predict the direction an equilibrium will shift when a stress is applied to it, and predict the resulting change in concentration of reactants and products. Equilibrium systems are dynamic, meaning they are constantly in motion. Equilibrium must be in a closed system, or the system cannot remain at equilibrium. But sometimes you don’t want your system to be at equilibrium! How irritating it would be if you went to all the trouble to make a product, just to have it decompose back into the reactants again and reach equilibrium! How can you force a system at equilibrium to do what YOU want it to? That’s right! Make equilibrium work for YOU!!! Le Chatelier's Principle If a system at equilibrium is subjected to a stress (any factor that affects reaction rate, like temperature, concentration and pressure for gases), the equilibrium will shift in a way that relieves the stress, in the direction of whichever reaction was made faster by the stress. This will cause a change in concentration of both the reactants and products until the equilibrium is re-established. FORWARD SHIFT Reactants Products REVERSE SHIFT Stress Shift Change In Concentration Adding reactant This increases the number of collisions between reactant particles, making the Reactants: decrease FORWARD reaction go faster. Products: increase Removing reactant This decreases the number of collisions between reactant particles, making the Reactants: increase REVERSE reaction faster than the forward reaction. Products: decrease Adding product This increases the number of collisions between product particles, making the Reactants: increase REVERSE reaction go faster. Products: decrease Removing product This decreases the number of collisions between product particles, making the Reactants: decrease FORWARD reaction faster than the reverse reaction. Products: increase This depends on the direction of shift. Increasing Temperature This favors the ENDOTHERMIC reaction, causing the equilibrium to shift AWAY FROM THE SIDE WITH HEAT to absorb the excess energy, Decreasing Temperature This favors the EXOTHERMIC reaction, causing the equilibrium to shift TOWARDS FROM THE SIDE WITH Increasing Pressure (gases only) Decreasing Pressure (gases only) HEAT to release energy, This causes the system to bring the pressure back down by shifting TOWARDS THE SIDE WITH FEWER MOLES OF GAS on it. This causes the system to bring the pressure back UP by shifting TOWARDS THE SIDE WITH MORE MOLES OF GAS on it. IF THE SHIFT IS TOWARDS THE PRODUCTS, THEN PRODUCTS WILL INCREASE AND REACTANTS WILL DECREASE. IF THE SHIFT IS TOWARDS THE REACTANTS, THEN REACTANTS WILL INCREASE AND PRODUCTS WILL DECREASE. © 2009, Mark Rosengarten AE 20
Catalysts, inhibitors and surface area have NO EFFECT on systems at equilibrium. They allow a system to get TO equilibrium faster, but once there, they affect both reactions equally, meaning that the equilibrium will not be changed. Application of Determining Direction of Equilibrium Shift For the equilibrium N 2 (g) + 3 H 2 (g) 2 NH 3 (g) + heat: Stress Shift Change In Concentration Add N 2 (g) FORWARDS N 2 : decreases Add a reactant, shift to products H 2 : decreases Remove N 2 (g) Add H 2 (g) Remove H 2 (g) Add NH 3 (g) Remove NH 3 (g) Increase Temperature Decrease Temperature Increase Pressure Decrease Pressure REVERSE Remove a reactant, shift to reactants FORWARDS Add a reactant, shift to products REVERSE Remove a reactant, shift to reactants REVERSE Add a product, shift to reactants FORWARDS Remove a product, shift to products REVERSE Increase T, shift away from heat FORWARDS Decrease T, shift towards heat FORWARDS Increase P, shift to side with fewer moles of gas REVERSE Decrease P, shift to side with more moles of gas For the solution equilibrium KNO 3 (s) + 34.89 kJ K +1 (aq) + NO 3 -1 (aq): NH 3 : increases N 2 : increases H 2 : increases NH 3 : decreases N 2 : decreases H 2 : decreases NH 3 : N 2 : increases H 2 : increases NH 3 : decreases N 2 : increases H 2 : increases NH 3 : decreases N 2 : decreases H 2 : decreases NH 3 : increases N 2 : increases H 2 : increases NH 3 : decreases N 2 : decreases H 2 : decreases NH 3 : increases N 2 : decreases H 2 : decreases NH 3 : increases What happens to the concentration of K +1 (aq) when the temperature is increased? N 2 : increases H 2 : increases NH 3 : decreases Stress: Increasing temperature Shift: Away from heat, FORWARDS Change In Concentration: Since the shift is TOWARDS K +1 , the concentration of K +1 INCREASES. What happens to the concentration of NO 3 -1 (aq) when the temperature is decreased? Stress: Decreasing temperature Shift: Towards heat, REVERSE Change In Concentration: Since the shift is AWAY from NO 3 -1 , the concentration of NO 3 -1 DECREASES. © 2009, Mark Rosengarten AE 21
Page 1 and 2: Kinetics, Thermodynamics and Equili
Page 3 and 4: FACTORS THAT AFFECT REACTION RATE B
Page 5 and 6: 2) Potential Energy Diagrams (HW: p
Page 7 and 8: Potential Energy Diagrams: graph th
Page 9 and 10: 3) Equilibrium Systems (HW: p. 28,
Page 11 and 12: For the equilibrium 2 SO 2 (g)+ O 2
Page 13 and 14: The more soluble the salt is, the h
Page 15 and 16: 2) ENTROPY - the randomness (disord
Page 17 and 18: The quantity ∆G is Gibbs Free Ene
Page 19: A/E Reference Table B Energies of F
Page 23 and 24: Student Name:______________________
Page 25 and 26: D) For the following blank PE Diagr
Page 27 and 28: H) Graph and label a potential ener
Page 29 and 30: 8) Complete the following chart: K
Page 31 and 32: D) For the formation of PbO: 1) Usi
Page 33: C) Complete the following questions

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