Chemical Equilibrium

Chemical Equilibrium - Chemical Equilibrium Chapter 13...

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Chemical Equilibrium Chapter 13 Zumdahl Chemical Equilibrium – the state where the concentrations of all reactants and products remain constant with time. If the equilibrium is said to lie to the right then the products are favored. If the equilibrium is said to lie to the left then the reactants are favored. Chemical equilibrium is a dynamic situation where for every product that returns to reactant an equivalent amount of reactant will become product. Equilibrium does not mean that the reaction has stopped. At equilibrium the forward and reverse reaction rates are the same. Factors determining equilibrium position – initial concentrations, relative energies of reactants and products, relative degree of organization of reactants and products. The law of mass action – a general description of the equilibrium condition. For a reaction: jA + kB ↔ lC + mD get an equilibrium expression [ ] [ ] [ ] [ ] k j m l B A D C K = , where [X] denotes concentration of X at equilibrium and K is a constant called the equilibrium constant that is specific to a reaction at a certain temperature. Summary of conclusions about the equilibrium expression: 1. The equilibrium expression for a reaction is the reciprocal of that for the reaction written in reverse. 2. When the balanced equation for a reaction is multiplied by a factor of n, the equilibrium expression is raised to the nth power and K new = (K original ) n . 3. K values are customarily written without units. Equilibrium position – a set of equilibrium concentrations. 1
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There is only one equilibrium constant for a given reaction at a given temperature, but there are infinite equilibrium positions, the equilibrium position depends on the initial concentrations while the constant does not. K p – the equilibrium constant defined using pressures rather than molarity as above. Can use pressures because of the ideal gas law where RT V n P = , and n/V is concentration in moles per liter. The values of K c or K as it is usually referred to as, and K p will be different, but are related by the relationship: K p = K c (RT) Δn , where Δn = (l + m) – (j + k). Homogeneous equilibria – all reactants and products in the same phase. Heterogeneous equilibria – reactants and products in different phases, pure solids and pure liquids will not effect the equilibrium and are not included in the equilibrium expression. The extent of a reaction can be determined by the magnitude of the equilibrium constant, the
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Chemical Equilibrium - Chemical Equilibrium Chapter 13...

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