Chemistry

• Crude oil:

  • Found in- Rocks: used to produce fuels
  • Mixture of compounds called hydrocarbons- NOT chemically combined
  • Formed from fossilised remains of ancient plankton
• Alkanes:

  • Alkanes are saturated hydrocarbons (saturated=molecule only contains single bonds)
  • Burn well- makes them useful fuels
  • General formula= CnH(2n+2)
• Electrolysis:

  • electric current passed through an electrolyte (liquid or solution that contains ions)- CAN conduct electricity
  • causes ions to move to electrodes -> to form pure elements
• ANODE = electrons LOST

  CATHODE = electrons GAINED
• Electrolysis: when ionic compound is molten:

  • Positive metal ions attracted to CATHODE; where they will GAIN electrons to form pure metal
  • Negative non- metal ions attracted to ANODE where they will LOSE electrons to form pure non- metal
• Electrolysis of aqueous solution:

  • requires less energy to dissolve IONIC compounds in water than to melt them
  • However, electrolysis of solutions pure elements not always produced-> water can also undergo ionisation:

  H2O[l] ~> H+[aq] + OH-[aq]
• Electrolysis of aqueous solutions- products at the ANODE:

  • if non- metal contains oxygen then oxygen gas is formed at anode ~~>

  . The OH-[aq] ions formed from ionisation of water are attracted to anode/ ions lose electrons to anode and form oxygen gas

  • if non- metal ion is halogen, then halogen gas formed at anode
• Electrolysis of aqueous solution: products at CATHODE:

  . If the metal is MORE reactive than hydrogen, hydrogen gas is formed at cathode:

  1. H+[aq] ions from ionisation of water attracted to cathode an react with it
  2. H+[aq] ions GAIN electrons from cathode an form hydrogen gas:

  2H+[aq] + 2e- ~> H2[gas]

  3. Metal ions remain in solution
• Ionisation of water: half equation

  H2O[l] ~> H+[aq] + OH-[aq]
• Electrolysis of aluminium oxide:

  • Aluminium is extracted from aluminium oxide by electrolysis:

  1. Aluminium oxide mixed with a substance called CRYOLITE (lowers the melting point)
  2. Mixture then heated until molten
  3. Resulting molten mixture undergoes electrolysis
• Electrolysis of aluminium oxide:

  Cathode: pure aluminium is formed

  Al3+[l] + 3e- ~> Al[l]

  Anode: oxygen is formed

  2O2-[l] ~> O2[g] + 4e-

  • In electrolysis of aluminium, anode is made of graphite
  • graphite reacts with oxygen to form CO2 and slowly wears away- needs to be replaced frequently
• Energy Changes:

  . during a chemical reaction, energy transfer by:

  • to the surroundings- EXOthermic
  • from the surroundings- ENDOthermic
• Energy changes- SURROUNDINGS:

  • if thermometer records an increase in temp, the reaction in test tube is EXOthermic
  • if thermometer records a decrease in temp, reaction= ENDOthermix
• Energy changes- Reaction profiles

  . Exothermic- reactants have higher energy than products

  • energy is released to surroundings

  . Endothermic- products have higher energy than reactants

  • energy is absorbed from surroundings
• Energy changes- Reaction profiles

  • Endothermic always has a larger amount of activation energy needed to break the bonds
• Exothermic summary:

  • releases energy
  • temp of surroundings increases
  • E.g oxidation, combustion and neutralisation
  • Uses= self- heating can, hand warmers
  • Bonds= more energy released when making bonds than required to break them
• Endothermic summary:

  • from the surroundings
  • temp of surroundings decreases
  • e.g thermal decomposition
  • Uses= sports injury packs
  • Bonds= LESS energy released when making bonds than required to break bonds
• Energy changes- BONDS:

  • Breaking bond requires energy so it’s endothermic
  • Making a bond releases energy so is exothermic
• Energy changes- BONDS:

  Breaking bonds:

  • If lots of energy released when making bonds and only a little required to break them~~> overall energy is released so its EXOTHERMIC

  Making bonds:

  • If LITTLE energy released when making bonds and lots is required to break them~~> overall energy is taken it so it’s ENDOTHERMIC
• Energy changes- Bond calculations:

  . To work out overall change of a reaction you must:

  1. find how much energy needed to break all bonds in reactants
  2. find out how much energy is released when making all bonds in products

  Overall energy transferred= energy required to break bonds-- energy required to make bonds
• Calc RATE OF REACTION:

  . How quickly reactant is used up

  • Mean rate of reaction= quantity of reactant used/ time taken

  . How quickly product is produced

  • Mean rate of reaction= quantity of products formed/ time taken
• Rate of reaction

  . reaction involving gas, can be measured by CHANGE IN MASS

  1. Reaction mixture placed on mass balance
  2. Gaseous product is given off
  3. Mass of flask will decrease

  Rate= change in mass/ time taken
• Rate of reaction:

  Reactions involving gas, measured by VOLUME OF GAS PRODUCED:

  1. Reaction mixture is connected to gas syringe
  2. Gas is collected during reaction

  Rate= volume of gas produced/ time taken
• Collision theory :

  . When particles collide, they must have a large activation energy to react
• Collision theory:

  Increasing rate of reaction:

  • Increasing FREQUENCY OF COLLISIONS
  • Increasing energy of particles when they collide
• Factors affecting rate of reaction:

  1. Increasing temp

  . HOW= heat container where reaction is occurring

  . WHY= 1) particles move faster, 2)particles have more energy

  (2 separate effects)
• Factors affecting rate of reaction:

  2. Increasing concentration of solutions

  • WHY= more reactant particles in reaction mixture so collisions become frequent

  3. Increasing pressure of gases

  • less space between particles
  • HOW= make container smaller
• Factors affecting rate of reaction:

  4. Increasing surface area of solids

  • HOW= cut solid into smaller pieces or grind to create powder
  • WHY= greater the surface area, more reactant particles exposed
• Properties of hydrocarbons:

  • Viscosity- Hydrocarbons with longer chains have higher viscosity
  • Boiling point- Hydrocarbons with longer chains have higher boiling points
  • Flammability- hydrocarbons with longer chains are less flammable
• Long chain hydrocarbons

  • Higher boiling points
  • Less flammable
  • Higher viscosity
• Burning hydrocarbons in a plentiful supply of oxygen:

  • Energy is released
  • Carbon dioxide is created
  • Water is created
• Short chain hydrocarbon fractions of crude oil burn easily because:

  • Highly volatile
  • Ignite easily
  • Have low boiling points
• Fractional distillation:

  • Products are fractions
  • Separates crude oil
• Fractional distillation:

  1. Evaporation- Crude oil is heated until it evaporates
  2. Condensation- Hydrocarbons condense at diff points in fractioning column
  3. Collection- Fractions are collected + then processed to create end products
• Carbon compounds:

  • Homologous series- a family of similar compounds
  • Organic compounds- carbon containing compounds
• Cracking: process where long chain hydrocarbons are broken down into shorter and more useful molecules
• Cracking:

  • Catalytic cracking

  . Catalyst / high temperature

  • Steam cracking

  . Steam / high temp

  BOTH PRODUCTS= alkanes and alkenes
• Alkene uses:

  1. Starting materials for many chemicals
  2. Being combined to make polymers