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Unformatted text preview: CHAPTER 17 Equilibrium: the extent of chemical reactions 17.1 The equilibrium state and the equilibrium constant Kinetics: speed of a reaction, the concentration of product that appears (or reactant that disappears) per unit time. Kinetics and equilibrium are not necessarily related = rate and extent of reaction not necessarily related. Given sufficient time, the concentrations of reactants and products no longer change b/c all reactions are reversible and reach a state of equilibrium. A system at equilibrium :- reactant and product concentrations are constant over time -the forward reaction rate equals the reverse reaction rate-the reaction quotient equals the equilibrium constant: Q = K Equilibrium: applies to the extent of a reaction, the concentrations of reactant product present after an unlimited time, or once no further change occurs. Reactant and product concentrations stop changing b/c the forward and reverse rates have become equal: At equilibrium: rate fwd = rate rev rate = k[A] m [B] n then , k forward [reactants] m = k reverse [products] n Equilibrium constant ( K ) : K = k fwd / k rev = [products] n / [reactants] m values of m and n are those of the coefficients in the balanced elementary chemical equation. The rates of the fwd and rev reactions are equal (not the concentrations of products and reactants). The magnitude of K is an indication of how far a reaction proceeds toward a product at a given temp:-small K: reaction yields very little product before reaching equilibrium, might even say there is “no reaction”. Little product formed, a lot of reactant remained at equilibrium.-large K: very little reactant remaining at equilibrium, large product. -intermediate K: when significant amounts of both reactant and product are present at equilibrium. 17.2 The reaction quotient and the equilibrium constant Law of chemical equilibrium (law of mass action) : at a given temp, a chemical system reaches a state in which a particular ratio of reactant and product concentrations has a constant value. For a particular system and temp, the same equilibrium state is attained regardless of how the reaction is run....
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