chem paper 2

• 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


  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
• Increasing the surface area of the reactants

  Means there are more exposed reacting particles, resulting in more frequent successful collisions so the rate of reaction increases
• Increasing the temperature


  Means the particles will have more kinetic energy and so will move faster, resulting in more frequent collisions, and a larger proportion of the particles will have at least the activation energy, so 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


  These reactions involve monomers with two functional groups. When these monomers react they join together and lose small molecules such as water
• Cracking


  A process that involves breaking down larger hydrocarbons to produce smaller more useful molecules. Cracking can be done by catalytic cracking or steam cracking
• DNA


  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


  A chemical process by which molecules such as glucose are broken down anaerobically. Ethanol is produced when sugar solutions are fermented using yeast
• Fractional distillation


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


  Long-chain hydrocarbons are heated to turn them into a gas. The hydrocarbon vapour is then mixed with steam and heated to a very high temperature which caused them to split into smaller molecules