Equilibria

Equilibria

1. Equilibrium

   • Types of equilibria
     • Solubilty
       • An equilibrium between a solute and a solvent in a saturated solution in a closed system
     • Phase
       • An equilibrium between different physical states of a pure substance in a closed system
     • Chemical rxns
       • An equilibrium between reactants and products of a chemical rxn in a closed system
   • Le Chatelier's Principle
     • Temp
       • In an endothermic reaction as the temperature increases the system shifts to the products and as the temperature decreases the system shifts to the left. Vice versa for and exothermic reaction
     • Concentration
       • An increase in concentration of a reactant or product will cause the system to shift the other way. A decrease of concentration in the products or reactants will cause the system to shift towards the decreased side.
       • The common ion effect will increase the concentration of an element
     • Catalyst
       • A catalyst will not shift the sytem at all, but will decrease the time that the system requires to reach equilibrium
     • Inert gas
       • Will not affect the equilibrium in any way
     • Volume/pressure
       • An increase in volume/decrease in pressure will result in the system shifting to produce more gas molecules. A decrease in volume/increase in pressure will cause the system to shift to reduce the amount of gas molecules
     • When a chemical system is disturbed by a change in property, the system adjust in a way that opposes the change

2. Predicting precipitation and equilibrium law

   • Equilibrium law
     • If Kc = Qc then the system is at equilibrium. If Qc<Kc then the system will shift to the right. If Qc>Kc then the system will shift to the left.
   • Predicting percipitation
     • If Q = Ksp the solution is saturated and no more solute can be dissolved. If Q<Ksp the solution is unsaturated and more solute can be added. If Q>Ksp the solution is supersaturated and extra solute will precipitate.

3. Acid-Base Equilibrium

   • Strong acid/base
     • A strong acid such as HCl or a strong base such as NaOH wll completely ionize in water
   • Weak acids/bases
     • A weak acid is an acid that does not completely ionize in water
       • Often needs the ionization constant for acid (Ka) to solve problems
     • Weak bases are bases that have a weak attraction to protons
       • Often needs the ionization constant for bases (Kb) to solve problems
   • Bromsted-Lowery Theory
     • An acid is a proton donor while a base is a proton accepter
     • Reactants and products vary by one hydrogen atom
   • Titration
     • A titration is a lab procedure where a precise amount of solution in a buret (the titrant) is added to a measured samle of solution. The purpose of this is to determine the concentration of a specified chemical in the sample
   • Buffers
     • A buffer occurs when there is an equilibrium between a weak acid and its conjugate base. In this equilibrium the pH remains relatively contant
     • Typically when hydrogen atoms are added to a buffer the system will shift towards the reactants and balance the pH
     • Typically when OH molecules are added to a buffer, the hydroxide molecules bind with any hydrogen toms and form water. The system then shifts towards the products to produce more hydrogen atoms and maintan the pH
   • Salts
     • Will not affect pH if the salt is formed from the cation of a strong base and the anion of a strong acid
     • Will be acidic if the it is the conjugate of a weak base
     • Will be basic if it is the conjugate of a weak acid
     • If it has an anion of a weak acid and a cation of a weak base then the Kb and Ka must be compared
     • Metal oxides will always be basic
     • non-metal oxides will always be acidic