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

LDF’s Temporary Dipoles caused by uneven distribution of electrons

Covalent molecular

Fullerene C 60 Lots of different sizes Discrete Molecules

Covalent network structure

Monatomic structure