Chemistry

Subdecks (2)

Cards (81)

  • 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