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UA CH 102 - Chemical Equilibrium continued
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CH 102 1st Edition Lecture 12 Outline of Current Lecture I. Equilibrium Expression for the Gas Phase Decomposition of Hydrogen IodideII. Dynamic EquilibriumIII. The Reaction QuotientIV. Kc and Kp ConnectionV. Le Châtelier’s Principle: Disturbing and Restoring EquilibriumVI. Disturbing Equilibrium: Adding ReactantsVII. Disturbing Equilibrium: Removing ReactantsCurrent Lecture I. Equilibrium Expression for the Gas Phase Decomposition of Hydrogen Iodide2 HI (g) → H2 (g) + I2 (g) II. Dynamic Equilibriuma. Dynamic equilibrium is the condition wherein the rates of the forward and reverse reactions are equal.b. Because the forward reaction slows and the reverse reaction accelerates, eventually they reach the same rate.c. Once the reaction reaches equilibrium, the concentrations of all the chemicals remain constant because the chemicals are being consumed and made at the same rate.d.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.III. The Reaction Quotienta.b. For Q < Ki. the reaction is not at equilibrium and it must go in the forward direction to reach equilibrium, reactants are consumed and product are formedc. For Q = Ki. the reaction is at equilibrium, there is not change in concentrationsd. For Q > Ki. the reaction is not at equilibrium and it must go in the reverse direction to reach equilibrium, products are consumed and reactants are formedIV. Kc and Kp Connectiona. In calculating Kp, the partial pressures are always in atm.b. The values of Kp and Kc are not necessarily the same because of the difference in units.c. Kp = Kc when Δn = 0d. The relationship between them is as follows:e. Kp = Kc × (RT)Δnf. Where Δn is the difference between the number of moles of reactants and the number of moles of products.V. Le Châtelier’s Principle: Disturbing and Restoring Equilibriuma. Once a reaction is at equilibrium, the concentrations of all the reactants and products remain the same.i. However, if the conditions are changed, the concentrations of all the chemicals will change until equilibrium is restored.b. The new concentrations will be different, but the equilibrium constant will be thesame, unless you change the temperature.c. Le Châtelier’s principle guides us in predicting the effects various changes in conditions have on the position of equilibrium. i. It says that if a system at equilibrium is disturbed, the position of equilibrium will shift to minimize the disturbance. ii. Disturbances all involve making the system open.VI. Disturbing Equilibrium: Adding Reactantsa. After equilibrium is established, a reactant is added, as long as the added reactant is included in the equilibrium constant expression.i. That is, as long as it is not a solid or liquid.b. How will this affect the rate of the forward reaction? i. Adding a reactant initially increases the rate of the forward reaction, but it has no initial effect on the rate of the reverse reaction. ii. The reaction proceeds to the right until equilibrium is restored.c. How will it affect the rate of the reverse reaction? i. At the new equilibrium position, you will have more of the products than before, less of the non-added reactants than before, and less of the added reactant. ii. But you will not have as little of the added reactant as you had before the addition.d. How will it affect the value of K?i. At the new equilibrium position, the concentrations of reactants and products will be such that the value of the equilibrium constant is the same.VII. Disturbing Equilibrium: Removing Reactantsa. After equilibrium is established, a reactant is removed, as long as the removed reactant is included in the equilibrium constant expression.i. That is, not a solid or liquidb. How will this affect the rate of the forward reaction? i. Removing a reactant initially decreases the rate of the forward reaction, but has no initial effect on the rate of the reverse reaction. 1. So the reaction is going faster in reverse.ii. The reaction proceeds to the left until equilibrium is restored. c. How will it affect the rate of the reverse reaction? i. At the new equilibrium position, you will have less of the products than before, more of the non-removed reactants than before, and more of the removed reactant.1. But you will not have as much of the removed reactant as you hadbefore the removal.d. How will it affect the value of K?i. At the new equilibrium position, the concentrations of reactants and products will be such that the value of the equilibrium constant is the same.VIII. The Effect of Concentration Changes on Equilibriuma. Adding a reactant will decrease the amounts of the other reactants and increase the amount of the products until a new position of equilibrium is found that has the same K.b. Removing a product will increase the amounts of the other products and decrease the amounts of the


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UA CH 102 - Chemical Equilibrium continued

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