Equilibrium

Equilibrium

1. Dyanamic Chemical Equilibrium

   • A state in which the rates of the forward and backward reactions are equal
     • Reaction doesn't cease simply for every mole of reactants that reacts a mole of products decomposes.
   • The ratio of the concentrations at equilbrium is equal.
     • Le Chatliers Principle
       • If a system is disturbed by a change in concentration pressure or temperature the system will adjust its equilibrium position to account for it.
         • Concentration
           • If the concentration of a substance is increased it will react to restore order
           • If the concentration of a substance decreases the reverse of the reaction happens to produce more of the substance.
         • Pressure
           • When pressure is increased ie more gas molecules per unit of space.
             • A reaction is favored that decreases the number of gas molecules ie the direction that contains the least total number of molecules.
           • When Pressure is decreased ie fewer molecules per unit of volume.
             • A reaction is favored that increases the number of molecules in the container.
         • Heat
           • Endothermic
             • Heat is treated as a reactant see concentation for details about that
           • Exothermic
             • Heat is treated as a product
   • Requries that no reactants or products escape.

2. The Equilibrium Constant

   • Molar Expression
     • Kc=([D]^d[E]^e)/([A]^a[A]^b
       • Where Kc=Equilbrium Constant The upper case letters are the concentration at equilibrium and their respective lower case letters are their coefiencts.
       • The numerator is the products the denomintor is reactants
       • Relation with chemical equation.
         • If an equation has been multiplied by a number then the eq constant is raised to that power.
         • If a chemical equation can be summarized as a net chemical equation (See Hess's Law) then the eq constant is the product of the kcs of the repective equations
         • If one of the substances is a pure solid or a pure liquid then it is omitted from the equilibrium expression.
           • If a solvent is one of the reactants and is in extreme excess it can be ignored as well.
   • Partial Pressure Expression
     • Same thing as molar expression except partial pressures instead of concentration
       • The values between Kc and Kp are different however they can be related using the following equation.
         • Kp=Kc(RT)^delta n.
           • Kp=the constant for partial pressures. Kc=the constant for molar concentration. R=Gas constant (.0821 L/mol) T=temperature in Kelvin. Delta n=the change in the number of moles of gaseous product gained or lost
   • Magnitude
     • Values for Kc
       • If Kc is much greater than 1 then the products are favored.
       • If Kc is much less than one then reactants are favored