Key Chem P2

• Activation energy

  The minimum amount of energy that particles must collide with to react
• Catalyst

  Catalysts increase the rate of reaction by providing a different pathway for the reaction that has a lower activation energy. They are not used up during the reaction.
• Collision theory

  According to this theory, chemical reactions can occur only when reacting particles collide with each other and with sufficient energy
• If the concentration of a reactant is increased

  More products will be formed until equilibrium is reached again
• If the concentration of a product is decreased

  More reactants will react until equilibrium is reached again
• An increase in pressure

  Causes the equilibrium position to shift towards the side with the smaller number of molecules
• A decrease in pressure

  Causes the equilibrium position to shift towards the side with the larger number of molecules
• If the temperature of an equilibrium system is increased

  The relative amount of products at equilibrium increases for an endothermic reaction and decreases for an exothermic reaction
• Increasing the concentration of reactants in solution

  Means the reacting particles will be closer together, so they will collide more often, resulting in a higher rate of successful collisions and a faster rate of reaction
• Increasing the pressure of gaseous reactants

  Means the reacting particles will be closer together, so they will collide more often, resulting in a higher rate of successful collisions and a faster rate of reaction
• Effect of surface area on reaction rate

  • Increasing the surface area of the reactants means there are more exposed reacting particles
  • This means there are more frequent successful collisions so the rate of reaction increases
• Effect of temperature on reaction rate

  • Increasing the temperature means the particles will have more kinetic energy and so will move faster
  • If the molecules are moving faster they will collide more often and, since they've gained kinetic energy, a larger proportion of the particles will have at least the activation energy
  • For both these reasons the rate of reaction increases
• Equilibrium

  When a reversible reaction occurs in apparatus which prevents the escape of reactants and products, equilibrium is reached when the forward and reverse reactions occur at exactly the same rate
• Le Chatelier's Principle

  If a reaction at equilibrium is subjected to a change in concentration, temperature or pressure, the position of equilibrium will move to counteract the change
• Rate of reaction

  • The measure of the amount of product formed or reactant used over time
  • The units of rate of reaction may be given as g/s, cm3/s or mol/s
• Reversible reaction

  • Reactions in which the products from the reaction can react together to form the original reactants
  • The direction of reversible reactions can be changed by changing the conditions
• Addition polymerisation

  A reaction where many small molecules (monomers) join together to form very large molecules (polymers)
• Alcohols

  Alcohols contain the functional group –OH. The first four members of a homologous series of alcohols are methanol, ethanol, propanol and butanol.
• Alkanes

  Alkanes are the most common hydrocarbon found in crude oil. Alkanes have the general formula CnH2n+2.
• Alkenes

  Alkenes are hydrocarbons with a double bond between two of the carbon atoms in their chain, causing them to be unsaturated. They have the general formula CnH2n.
• Amino acids

  Amino acids have two different functional groups in a molecule. They react by condensation polymerisation to produce polypeptides.
• Carboxylic acids

  Carboxylic acids have the functional group –COOH. The first four members of a homologous series of carboxylic acids are methanoic acid, ethanoic acid, propanoic acid and butanoic acid.
• Catalytic cracking

  Long-chain hydrocarbons are heated to turn them into a gas. The vapour is then passed over a hot powdered aluminium oxide catalyst. The long chain molecules split apart on the surface of the catalyst.
• Combustion

  Combustion of hydrocarbon fuels releases energy. During combustion, the carbon and hydrogen in the fuels are oxidised.
• Complete combustion

  Water and carbon dioxide are the only products of the complete combustion of a hydrocarbon.
• Crude oil

  A finite resource found in rocks. It is the remains of an ancient biomass consisting mainly of plankton that was buried in mud. Most of the compounds in crude oil are hydrocarbons.
• Condensation polymerisation

  Monomers with two functional groups react, join together and lose small molecules such as water
• Cracking

  1. Breaking down larger hydrocarbons to produce smaller more useful molecules

  2. Can be done by catalytic cracking or steam cracking
• DNA

  • Encodes genetic instructions for the development and functioning of living organisms and viruses
  • Most DNA molecules are two polymer chains, made from four different nucleotides, in the form of a double helix
• Esters

  • The product of a condensation reaction between a carboxylic acid and alcohol
  • For example: ethanol + ethanoic acid → ethyl ethanoate
• Fermentation

  1. A chemical process by which molecules such as glucose are broken down anaerobically

  2. Ethanol is produced when sugar solutions are fermented using yeast
• Fractional distillation

  1. A method of separating a mixture of substances according to their different boiling points

  2. Commonly used to separate crude oil into different fractions
• Homologous series

  A series of compounds with the same functional group and similar chemical properties
• Hydrocarbons

  Molecules that are made up of hydrogen and carbon atoms only
• Nucleotides

  The monomers which make up DNA
• Polyesters

  • A category of polymers which contain the ester functional group in their main chain
  • Formed from condensation polymerisation
• Polymers

  Large long-chain molecules made up of lots of small monomers joined together by covalent bonds
• Polypeptide

  A chain of amino acids
• Repeat unit

  The part of a polymer whose repetition would produce the complete polymer chain
• Steam cracking

  1. Long-chain hydrocarbons are heated to turn them into a gas

  2. The hydrocarbon vapour is then mixed with steam and heated to a very high temperature which caused them to split into smaller molecules