chemical equilibrium

chemical equilibrium - Chapter 9: Chemical Equilibrium...

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Chapter 9: Chemical Equilibrium Equilibrium is important because usually reactions do not go to completion, but the reaction seemingly stops Equilibrium is characterized by an equilibrium constant. By controlling concentrations, temperatures and pressures, we can control what products are produced and how much of them. o For example: 3 H 2 (g) + N 2 (g) ó 2 NH 3 (g) If we first throw 3:1 ratio of hydrogen gas to nitrogen gas, and measure the immediate concentrations, the [H] and [N] will be very high, and [NH3] will be very low. However, if the concentrations were measured after a while, the concentrations of N and H would have decreased, and the concentration of NH3 would have increased. Equilibrium state is DYNAMIC. This means that although it appears that there is no change in concentration, in reality there an equal rate of products reactants as reactants products. Note: equilibrium is different than steady state. Steady state is a replenished source of a substance, which is replenished from outside your system. o i.e. vessels in the lung have a steady state of oxygen in order to oxygenate the blood. This creates a constant gradient, which is replenished by our breathing. Empirical Law of Mass Action: irrespective of initial concentrations, for a given reaction at equilibrium , the equilibrium constant: o You can also replace the concentrations with pressures for gasses to get the law of mass action for gas-phase reactions Significance of empirical law of mass action: o Inherent property of chemical reaction and does not depend on the initial concentrations o Its magnitude gives direct information of the equilibrium state or position of the reaction. If the equilibrium constant is small, then the concentrations of the
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This note was uploaded on 10/26/2011 for the course CHEM 20B taught by Professor Felker during the Spring '08 term at UCLA.

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chemical equilibrium - Chapter 9: Chemical Equilibrium...

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