CfE Higher Supported Study Week 1 Rates of Reaction Bonding in first 20 elements Key Areas Controlling the Rate Importance of controlling rate Collision theory to explain effects of Concentration Pressure Surface Area Temperature Collision Geometry Relative Rate Calculations Reaction Profiles/Potential energy diagrams Exothermic/Endothermic Activation Energy/Activated Complex Catalysts Temperature /Energy Distribution Diagrams Importance of controlling rate Industrial Processes Rate too low Not economically viable Rate too High Risk of thermal explosion Collision theory to explain effects of Concentration Increased concentration more particles in same space As more particles more likely to have collisions Collision theory to explain effects of Pressure Increased pressure more particles in smaller space As more particles more likely to have collisions Collision theory to explain effects of Surface Area Smaller particles = larger surface area More particles available to react and collide Collision theory to explain effects of Collision Geometry Particles must collide not only with enough energy (energy greater than or equal to the activation energy) But also Correct Geometry Relative Rate Calculations Rate = 1/t (units s -1 ) So. Time = 1/rate (units) Watch out for scales on graph answer not always obvious one Enthalpy Exothermic changes cause heat to be released Endothermic changes cause absorption of heat from surroundings (temp decrease) H = P - R H -ve H +ve Reaction Profiles Forwards Reaction Vs Reverse Reaction Activation Energy/Activated Complex Activation energy is the minimum kinetic energy required by colliding particles before reaction can occur Catalysts Catalysts are the only thing which lowers activation energy Effect of Temperature Temperature is measure of the average kinetic energy of a substance Effect of T on rate can be explained in terms of an increase in the number of particles with energy greater than activation energy. Temperature /Energy Distribution Diagrams Be able to add curve to graph Answer questions about temp affecting Activation energy/no. of collisions (Do you need graph for this) Key Areas Bonding and Structure in first 20 elements Metallic Covalent Molecular Covalent Network Monatomic Metallic Metallic structure consists of giant lattice of positively charged ions and delocalised outer electrons Covalent Non metals Sharing Electrons Attraction between positive nuclei and negative shared electrons. Covalent molecular consists of discrete molecules held together by weak London dispersion forces Phosphorus P 4 Sulphur S 8 LDFs Temporary Dipoles caused by uneven distribution of electrons Covalent molecular Fullerene C 60 Lots of different sizes Discrete Molecules Covalent network structure Monatomic structure