Paper 2

• How quickly a reaction happens is called the rate of reaction
• Rate of reaction

  The change in a quantity divided by time
• Mean rate

  Technically gives you the mean rate as the rate could be changing over the time you measure
• Experiment on rate of reaction

  Reacting hydrochloric acid and sodium thiosulfate in a conical flask over a piece of paper with a cross on it, measuring increased turbidity as the product forms
• Experiment on rate of reaction

  Measuring the volume of gas produced using a gas syringe connected to the reaction vessel
• Graph of gas volume produced over time

  Starts off steeply, then levels out or plateaus when the reaction is completed
• Finding the rate at any time

  Draw a tangent at that point on the graph and calculate the change in quantity divided by time
• Factors that increase the rate of a reaction

  Increasing concentration of reactants in solution, increasing pressure of gas reactants, increasing surface area of solid reactants, increasing temperature, adding a catalyst
• Reversible reactions allow products to return to their original reactants
• Example of a reversible reaction

  The Haber process where hydrogen and nitrogen react to make ammonia, which can also break down back into the separate gases
• In a closed system, both forward and reverse reactions will continually take place until equilibrium is reached
• Le Chatelier's principle

  If a system at equilibrium is subjected to a change, the system will adjust to counteract that change
• Increasing pressure in a reaction

  Favors the forward reaction until equilibrium is reached, shifting the position of equilibrium to the right
• Reducing pressure in a reaction

  Shifts the position of equilibrium to the left
• Changing concentration in a solution

  Follows the same principle as changing pressure in a reaction
• Proportion of ammonia increases

  Position of equilibrium shifts to the right
• Reducing pressure

  Shifts the position of equilibrium to the left
• Concentration in solutions

  Follows the same principle as pressure in shifting the equilibrium position
• Removing molecules from one side of a reaction

  Shifts the position of equilibrium in that direction to produce more
• Increasing temperature


  Makes it harder for a reaction to produce heat, favoring the endothermic reaction
• Higher temperature favors endothermic reactions


  As it supplies the energy required for the reaction
• Colder temperature favors exothermic reactions

  As it favors the forward reaction which is endothermic in this case
• Breaking down of reactant in a reaction

  Endothermic reaction
• Forward reaction is exothermic


  Reverse reaction must be endothermic and vice versa
• Organic compounds have carbon forming the backbone of the molecules
• Crude oil is found underground and is the result of Plankton being buried under water a long time ago
• Crude oil consists mostly of hydrocarbons, molecules made up of carbon and hydrogen atoms
• Most hydrocarbons in crude oil are alkanes, chains of single covalently bonded carbon atoms surrounded by hydrogen atoms
• General formula for alkanes is CNH2N+2
• All alkane names end with 'ane' and the beginning of the name indicates the chain length
• Fractional distillation is used to separate different length alkanes in crude oil
• Longer alkanes have higher boiling points due to stronger intermolecular forces
• Shorter alkanes remain as gases at the top of the fractionating column
• LPG contains a range of chain length alkanes, up to four carbons long
• Petrol is used in cars, kerosene for jet fuel, diesel oil for cars and lorries, and heavy fuel oil for large ships
• Complete combustion of alkanes with oxygen produces carbon dioxide and water
• Longer fractions of alkanes are more viscous, while shorter fractions are more flammable
• Alkene is a hydrocarbon with a carbon-carbon double bond, making it unsaturated
• Bromine water can be used to test for alkenes, turning colorless if an alkene is present
• Alkenes can be saturated by adding water to form alcohols