Chemistry 2b

Chemistry 2b

1. Rates of Reaction

   • Reaction rate=amount of reactant used up /time
     • Could measure (at timed intervals)...
       • Volume of gas formed
       • Number of bubbles formed
       • Time of for one reactant to dissolve
   • What effects it?
     • Temperature
       • Increases energy and therefore kinetic energy
     • Concentration
       • Increase collision freqeuncy
         • more particles for same volume
     • surface area
       • Collisions occur on surfaces
     • Catalysts
       • Include transition metals and their compounds
         • Different in different reactions
       • Reduce costs in industrial reactions
         • Molecules absorbed on catalyst surface
   • Reaction types
     • Exothermic
       • energy to surroundings
     • endothermic
       • energy from surroundings
     • Reversible= Exothermic one way, endothermic the other
       • Equilibrium occurs when reactions occur at same rate/both directions
         • Depends on conditions e.g. temperature
   • Yield
     • The amount of product obtained in a reaction
       • Better if:
         • Exothermic
         • High pressure
         • removing products and replenishing reactants

2. Electrolysis

   • Free ions
     • metals= positive
       • move to neg. electrode
         • Cathode
     • Non-metals= negative
       • move to pos. electrode
         • Anode
     • When molten, free to move
   • Equations
     • 1/2 equations
       • Represent oxidations and reductions
         • e.g. Sodium chlordie
           • Na+ (aq) + e- --> Na (s)
             • Reuction, pos/neg charge cancel out
             • Na+ gains 1 electron, has no charge
           • 2Cl-(aq)-->Cl2 (g) + 2e-
             • Oxidation, neg/pos charge balanced
             • 2cl- loses 2 electrons
   • Uses
     • If the metal in the reaction...
       • Is less reactive than hydrogen
         • Metal comes out at cathode
         • Hydrogen stays in solution
           • any metal more reactive than hydrogen can react with an acid
       • Is more reactive than hydrogen
         • We get hydrogen!
         • Metal stays in solution
     • Sulfate solutions give oxygen at anode

3. Salts, Acids and Alkalis

   • Bases
     • metal oxides and hydroxides
     • React with acids
     • Make salts
       • acid+metal=metal salt+hydrogen
       • acid+ammonia= ammonium slat
       • acid+soluble/insoluble base=metal salt +water
   • Ammonia forms alkaline solution in water
     • Would be good fertiliser, except to alkaline
       • React with acid and get neutral salt- perfect
   • All acids contain hydrogen ions
     • H+
   • All Alkalis contain Hydroxide ions
     • OH-
   • In neutralisation reactions...
     • Hydrogen and hydroxide ions react to make water
     • They always produce a salt
   • Precipitates
     • Insoluble salts- can be made as precipitates
     • Iron impurities
       • make into insoluble salts to remove from water