CHEM EQUILIBRIA

• Chemical equilibria


  Reversible chemical reactions where the reactants create the products which then go back and create the reactants
• Dynamic equilibrium


  When the rates of the forward and reverse reactions are the same
• In dynamic equilibrium, chemistry is happening but because the reactions are happening at the same rate there doesn't appear to be any activity
• Stoichiometry


  Used to discuss limiting reagents and how much of the products to expect, but only for unidirectional reactions
• Calculating equilibrium concentrations


  1. Set up an ICE (Initial, Change, Equilibrium) table

  2. Plug in known values

  3. Solve for the unknown x

  4. Use x to determine all equilibrium concentrations
• Equilibrium constant (Kc)


  Ratio of product concentrations (raised to power of stoichiometric coefficients) to reactant concentrations (raised to power of stoichiometric coefficients)
• Reaction quotient (Q)


  Calculated using non-equilibrium concentrations to predict the direction a reaction will go to reach equilibrium
• Solids and pure liquids are not included in the equilibrium constant expression
• When Kc equals Q, the system is at equilibrium
• For every 2 moles of reactant consumed, 1 mole of each product is formed
• Equilibrium


  Balance in a natural system
• When the balance of some natural system gets disrupted, we say that it's out of equilibrium
• Nature usually finds a way to restore the balance
• There's no reason that I can't enjoy the occasional hot pocket without destroying my so-called balanced diet, I just have to be sure to eat something that wasn't prepared in a salty lard factory to balance it out
• Forward reaction


  Reactants reacting to form products
• Reverse reaction


  Products changing back into the reactants
• When the forward and reverse reactions occur at the same rate, that's called chemical equilibrium
• Most chemists make their living using tricks to prevent chemical equilibrium, to knock it out of whack, maximizing the concentrations of the chemicals they want to produce at the expense of the balance that nature usually seeks
• The Haber process for making ammonia from nitrogen in the air really exists as an equilibrium
• Le Châtelier's Principle


  If stress is placed on a system that is at equilibrium the system will proceed in a direction that minimizes the stress
• Changing the concentration of any substance in a reaction

  Causes it to proceed in whatever direction restores the former balance
• Increasing the pressure


  Puts more stress on the high volume reactants than the low volume products, so the reaction shifts to the right, producing more ammonia than it does at low pressure
• Decreasing the pressure


  Has the opposite effect, the reaction proceeds in the direction that raises the pressure back to where it was before
• Endothermic reactions (consume heat)


  Are favored if heat is added so higher temperatures tend to feed endothermic reactions
• Exothermic reactions (release heat)

  Fair better at low temperatures
• Adding hydrochloric acid increases the chloride ion concentration and pushes the cobalt ion reaction to the right, the blue side
• Adding water pushes the cobalt ion reaction right back to the left, pink
• Raising the temperature


  Is like adding a reactant so the cobalt ion reaction will proceed to the right
• Lowering the temperature


  Is like taking away some reactants so the cobalt ion reaction proceeds to the left
• Acid


  Something that donates a proton
• Base


  Something that accepts a proton
• Proton


  H+ ion, the nucleus of a hydrogen atom after losing an electron
• Proton transfer


  1. Acid donates proton

  2. Base accepts proton

  3. Conjugate acid-base pair formed
• Protic species


  Molecules with hydrogen atoms that can be lost as protons
• Aprotic species


  Molecules that also display acidity and basicity
• Lewis base


  Donates a pair of electrons
• Lewis acid


  Accepts electrons
• Amphoteric


  Can act as both a Brønsted-Lowry acid and base
• Amphoteric substance


  • Water
• Acid-base reaction in water

  1. Proton transfer between water molecules

  2. Equilibrium