Chem 222 notes Week 5
Chem 222 notes Week 5 Chem 222
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This 2 page Class Notes was uploaded by Leslie Pike on Friday February 26, 2016. The Class Notes belongs to Chem 222 at Western Kentucky University taught by Darwin Dahl in Spring 2016. Since its upload, it has received 14 views. For similar materials see College Chemistry 2 in Chemistry at Western Kentucky University.
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Date Created: 02/26/16
This week begins Chapter 14. A system is at equilibrium when there is no observable change with time. The reaction going from the reactants to the products is equal to the reaction going from the products to the reactants. For some reactions, there is no equilibrium point, the reaction goes until all reactants are used up. Ex. 2H 2 O 2H O 2 For other reactions, they can go both ways: N 2 4======> 2NO (that is 2upposed to be two arrows but sometimes Microsoft Word can only do so much…) Equilibrium can be physical equilibrium, such as water or mercury in a closed container at equilibrium with its vapor. Equilibrium can be chemical, such as in the reaction shown above. For a reaction aA + bB cC + dD, the equilibrium constant is determined as: c d [C] [D] K= a b [ A] [B] K is unitless because it is a ratio. K can be written as Kc, the concentration equilibrium constant. At a homogenous equilibrium, all reactants are in the same phase. For a heterogeneous equilibrium, the reactants are in different phases. For gases, there is a pressure equilibrium constant (the partial , Kp, in addition to the concentration equilibrium constant. One can convert between the two with the following equation: Kp=Kc(RT) Δ n Here, Δn is the change in the number of moles of gas, or the number of moles of gas on the right minus the number of moles of gas on the left. It can be a negative number. R is 0.0821 L*atm/(mol*K) Q can be found by taking the equation for K and plugging in the initial concentrations of the reactants and products. If Q is grcater than K, the reaction will go to the left because there are too many products. If Q is less than K, the c reaction will go to the right because there are too many reactants. If Q = K, c equilibrium is reached and nothing happens. To work an equilibrium problem, remember ICE: Initial, Change, and Equilibrium. Initial is your initial concentrations. Change is how they change (multiply by balancing coefficient, and use a positive or negative sign in front depending on whether the species is being produced or consumed). Equilibrium is the final concentrations (initial concentrations plus or minus however much they changed).
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