chemistry paper 2

• 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
• reactions are rapid initially because we have a large number of reactant molecules
• the activation energy is the minimum amount of energy that the particles must have in order to react
• increasing the temperatures increases the rate of chemical reactions
• each collision has more energy due to the temperature increase
• 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
• the rate of the reaction depends on the number of particles that have enough energy to cross the activation energy barrier and collide successfully
• catalysts increase the rate by providing a different pathway for the reaction that has a lower activation energy
• we do not include catalysts in the chemical equation for a reaction. that is because they are not used up in the reaction.
• catalysts are not a reactant
• different reactions need different catalysts
• enzymes act as catalysts in living organisms
• 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 change the concentration of the reactants or products, then the system is no longer at equilibrium
• the concentrations of all the substances will change until the equilibrium is reached
• if we decrease the concentration, the system is no longer at equilibrium
• if a system is at equilibrium and a change is made to the conditions, then the system responds to counteract the change
• when the reverse reaction takes place, energy is taken in and the temperature of the system decreases
• if we increase the temperature of a system, then the equilibrium shifts to the left to reduce the temperature
• pressure affects reactions involving gasses
• 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
• if the number of molecules is the same on both sides, changing the pressure has no effect on the position of equilibrium
• we find crude oil in rocks
• crude oil is a finite resource
• crude oil is formed over millions of years from the remains of tiny sea creatures called plankton which are buried in mud
• crude oil is a mixture of molecules called hydrocarbons
• alkanes have a formula CnH2n+2
• methane has 1 carbon atom so contains 4 atoms of hydrogen
• ethane has 2 carbon atoms and 6 atoms of hydrogen
• propane has 3 carbon atoms and 8 atoms of hydrogen
• butane has 4 carbon atoms and 10 atoms of hydrogen
• short chain hydrocarbons are extremely flammable
• long chain hydrocarbons are very difficult to burn
• short chain hydrocarbons have a low boiling point
• very long chain hydrocarbons have a very high boiling point