Paper 2 - C8-C12

• The steeper the slope, the faster the reaction.
• Initially, the reaction is very fast. We are making a lot of product in a short amount of time. That is because we have a large number of reactant molecules so lots of them are reacting and forming the product.
• Gradually, the slope of the line becomes less steep. This tells us that the reaction is slowing down which means that the rate of reaction is decreasing. That is because a lot of the reactant molecules have already reacted and turned into product. This means that there are fewer reactant molecules available to react.
• At the end, the slope of the line is zero as the line is flat. At this point, the reaction has topped. All of the reactant molecules have already reacted.
• Mean rate of reaction = Quantity of product formed / Time
• Collision theory


  Chemical reactions can only take place when the reacting particles collide with each other. The collisions must have sufficient energy. The rate of a chemical reaction is determined by the frequency of successful collisions.
• Frequency


  The number of successful collisions per second.
• Because the rate increases if we increase the concentration, the rate is proportional to the concentration.
• The particles in a solution can only react with particles on the surface area of the solid.
• Because we have more collisions per second, the rate increases when we increases the surface area of a solid reactant.
• Smaller sized blocks of a solid reactant have a great surface area to volume ratio than larger blocks. This means that they have more particles on the surface so there are more collisions per second. This increases the rate of reaction.
• The activation energy is the minimum amount of energy that the particles must have in order to react (ie. collide successfully).
• Increasing the temperature increases the rate of chemical reactions. That's because increasing the temperature increases the energy of the particles. Because the particles now have more energy, they can now move faster. This increases the frequency of collisions. Each collision also has more energy which means that more particles can overcome the activation energy barrier and collide successfully.
• Because the rate of reaction increases with temperature, we can say that the rate of reaction is proportional to the temperature.
• Catalysts increase the rate of chemical reactions but are not used up during the reaction.
• Catalysts allow us to carry out reactions quickly without needing to increase the temperature which saves money. Because catalysts are not used up during the reaction, we can reuse them again and again.
• Catalysts increase the rate by providing a different pathway for the reaction that has a lower activation energy.
• A reversible reaction allows products to react and reform the original reactants.
• For ammonium chloride, we can make the reaction go forwards by heating it and we can make the reaction go backwards by cooling it down.
• If a reversible reaction is exothermic in one direction, it is endothermic in the opposite direction. The same amount of energy is transferred in each case.
• If we were to carry out a reversible reaction in a sealed container (to stop any reactants or products escaping), at some point, the forward and reverse reactions will take place at exactly the same rate. This point is known as equilibrium.
• If a system is at equilibrium and a change is made to the conditions, then the system responds to counteract the change. This is known Le Chatelier's Principle.
• If an increase of concentration is made to one side of the reversible reaction, the more of the other side is formed until equilibrium is reached again.
• If we increase the temperature of a system, then the equilibrium shifts to the left to reduce the temperature. That is because the reverse reaction is endothermic, so energy is taken, causing the temperature to fall.
• The pressure of a gas depends on the number of molecules. If we increase the pressure on a reversible reaction at equilibrium, the position of the equilibrium shifts to the side with the smaller number of molecules.
• If we reduce the pressure, then the position of the equilibrium shifts to the side with the larger number of molecules.
• We find crude oil in rocks and crude oil is a finite resource (it will eventually run out if we keep on using it).
• Crude oil is formed over millions of years from the remains of tiny sea creatures called plankton which were buried in mud.
• Crude oil is a mixture of molecules called hydrocarbons.
• Hydrocarbons are molecules made up of hydrogen and carbon atoms only.
• Alkanes have the general formula: CnH2n+2
• If we know the number of carbon atoms in the alkane (n), then we can calculate the number of hydrogen atoms.
• Alkanes are saturated molecules. That is because the carbon atoms are fully bonded to hydrogen atoms.
• Methane = CH4

  Ethane = C2H6

  Propane = C3H8

  Butane = C4H10
• Viscosity tells us the thickness of a fluid. Fluids with a high viscosity flow slowly
• As the size of the hydrocarbon molecules increases, the molecules get more viscous.
• Long chain hydrocarbons are extremely viscous.
• Flammability tells us how easily a hydrogen combusts (burns).
• Short chain hydrocarbons are extremely flammable.
• As the size of the hydrocarbon molecules increases, the molecules get less flammable.