Unit 3 - Chemical Reactions - created from Mind Map

The UK Chemical Indusrty Main Categories Stages Location Process Stages in Manufacture Costs pharmaceuticals petrochemicals & polymers paints & pigments speciality chemicals inorganics & fertilisers 1) Raw Materials: fossil fuels, metallic ores, minerals, air, water 2) Feedstock: a reactant from which other chemicals are extracted or synthesised 3) Reactor: feedstock converted into product, batch or continuous 4) Separation: evaporation, distillation, absorption, condensing, precipitation, filtration, drying historical/practical: transport routes, existing industries - ease of access to feedstocks safety/environmental: release of by-products into atmosphere/water systems Batch Continuous Pros: variety of products, plants less expensive to build, can be used for slow reactions, reactants can be in any state Cons: labour intensive, lost production when filling/emptying reactors, lost production when changing from 1 product to another because reactors often need to be cleaned small quantities of chemicals, pharmaceuticals, dye-stuffs, pesticides single products, operate year round, petrochemicals, ammonia, sulphuric acid Pros: less labour intensive, quality control of products more easily ensured, continuous operation makes for economic efficiency because shut downs are rare Cons: specific feedstock, plants expensive to build, solid reactants need to be in a fine powder because larger particles black pipes 1) Research/Development: identification of new product, development of suitable process 2) Pilot Study: scaled down version of plant, product quality, health hazards & costs are evaluated 3) Scaling Up: planning & development of a full scale plant 4) Production: new product manufactured 5) Review: processes are reviewed, modifications made, attempts made to reduce costs, hazards to health, safety & enviroment Capital: initial cost of building plant, research, development & associated structure Fixed: salaries, maintenance(depreciation), sale expenses Variable: cost of raw materials, distribution of product, energy costs & waste product treatment/disposal

Chemical Reactions Hess' Law Enthalpy the enthalpy change is independent of the route taken the enthalpy of the direct route is the same as the indirect route /\H = /\H2 + /\H3 combustion: 1 mole burns completely in oxygen solution: 1 mole of a substance dissolves in water neutralisation: acid is neutralised to form 1 mole of water

Equlibrium Dynamic Equilibirium Concentration Other fatcors Haber Process concentrations of reactants & products are constant rate of forward & backward reaction are equal Addition of reactant Addition of product Removal of product alkalis react with H+ ions to make water - removing them from the equilibrium, acids react with OH- ions increase in concentration of products rate of forward reaction increases moves to the right increase in concentration of reactants rate of backwards reaction increases moves to the left increase in concentration of products rate of forward reaction increases moves to the right Temperature Pressure Catalysts decrease in temp. favours exothermic increase in temp. favours endothermic increase in pressure favours side with less gas molecules decrease in pressure favours side with more gas molecules increase the rate of both reaction does not effect the position of equilibrium but means it is achieved more quickly ammonia produced by the reaction of nitrogen & hydrogen in the presence of an iron catalyst Conditions for Max. Yield Chemical Plant Conditions 1) after leaving the reaction chamber, the gaseous mixture is passed through a condenser, liquid ammonia is constantly removed, reducing the rate of the backward reaction 2) unreacted hydrogen & ammonia gases are recycled, increasing the rate of the forward reaction 3) because the forward reaction is exothermic & has fewer gas molecules present, the pressure will be low. high pressures & low temperatures will produce the greatest yield higher temp. than ideal because the reaction takes too long at low temp.s, the cost of running a plant at high pressure is is high, so the pressure is lower than ideal

Acids & Bases pH is a measure of H+ concentration in a solution Water Equilibrium Equilibrium in acids & alkalis Strong & Weak Acids All the concepts of strong & weak acids are the same for bases but with OH- ions instead of H+ ions Salt Solutions water partially dissociates to form H+ & OH- ions poor conductor of electricity due to small no. of ions at equilibrium concentration of [H+] & [OH-] is equal (1 X 10^-7 mol^-1) ionic product of water (Kw) = the multiple of the concentration of [H+] & [OH-] ions in 1 mole of watrer Kw = [H+] X [OH-} = (1 X 10^-7 mol l^1) X (1 X 10^-7 mol l^-1) =1 X 10^-14 mol^2 l^-2 must all add up to 1 X 10^-14 acid is a H+ donor , results in an increase in H+ ions & a decrease in OH- ions and an alkali does the opposite pH 1 = 1 X 10^-1 H+ ions (0.1 mol l^-1) & 1 X 10^-13 OH- ions (0.0000000000000001 mol l^-1) Strong: fully dissociated in dilute solution (ionised) due to polar covalent nature of acid molecule. Weak: partially dissociated in a dilute solution pH: strong acids have a lower pH because they have a greater concentration of H+ ions Conductivity: increases with the number of ions present, therefore strong acids have a higher conductivity Reactions: strong acids fully dissociate and therefore have excess H+ ions which react. weak acids don't have H+ ions in excess but as the H+ ions react the equilibrium position changes & more H+ ions are released to react. so strong acids react faster but both acids give the same volume & mass of product hydrochloric, sulphuric, nitric ethanoic, citric, carboxylic strong acid + strong base = neutral solution when an acidic salt dissolves in water it forms an acidic solution Soap is formed from the hydrolysis of fats & oils weak acid + strong base = alkaline solution strong acid + weak base = acidic solution the weak ion in the salt reacts with the OH- ions - taking them out of the water equilibrium mixture these ions must be replaced, so water molecules break down to replace the OH- ions & produce H+ ions at the same time this results inn excess H+ ions and an acidic solution is formed This is the same as for alkaline salts but the other way around fats & oils are made from glycerol & fatty acids fatty acids are carboxylic acids which are weak fats & oils are boiled in sodium hydroxide (strong base) to produce soap therefore, soaps are salts formed from a weak acid & a strong base - soaps dissolve in water to form an alkaline solution

Redox Reactions during redox reactions, one species is oxidised &n another is reduced Writing Redox Oxidation Is Loss Reduction Is Gain Agents oxy anions Redox Titrations Electrolysis displacement reactions are an example of redox reactons balance electrons combine oxidising agents accept electrons - it is reduced reducing agents donate electrons - it is oxidised negative ions which contain oxygen combined with another element 1) balance the non-oxygen element 2) balance oxygen with water molecules 3) balance hydrogen in water molecules by adding H+ ions 4) balance the charges on either side by adding electrons the concentration of a reactant can be calculated by the results of a redox titration 1) identify the 2 substances involved in the calculation & work out the mole ratio this equation can also be used 2) place all the information from the passage under appropriate headings (volume etc.) 3) calculate the no. of moles from the species for which you know all the data 4) using mole ration, calculate the no. of moles for the other substance 5) calculate the concentration of the substance you worked out the no. of moles for in step 4 C1V1/n1 = C2 V2/n1 when a current of electricity is passed through an ionic solution, the compound is broken down to produce its elements e.g. the electrolysis of CuCl(aq) produces copper & chlorine Electrodes Quantitive Electrolysis negative positive reduction takes place a solid is produced oxidation takes place gas produced Faraday's Number - Faraday's Law states that the no. of moles of a substance produced at an electrode during electrolysis is proportional to the no. of moles of electrons transferred to the electrode calculating mass/volume produced calculating time taken to produce a known mass/volume calculating what current is required to produce a known mass/volume the amount of electrical charge carried by 1 mole of electrons is 96500C (F) the no. of coulombs of charge going through a solution or melt can be calculated using the following formula: Q (coulombs) = I (current in amps) X t (time in seconds) e.g. Na+(aq) + e- = Na(s) 1 mole of electrons produces 1 mole of sodium 1 X 96500C 1) calculate the no. of coulombs of charge 2) write the ion electron equation & identify the mole ratio (electrons to solid) 3) using the mole ration, calculate the mass of the solid e.g. mole ratio of 3:1 would mean 1 X GFM if mole ratio is 3:1, (3 X 96500) = (1 X GFM) (mole ratio 3:1) therefore, Q X (1 XGFM) / (3 X 96500) = mass of solid 1) write ion electron equation & determine mole ratio (between reactant & electrons) 2) use mole ratio to determine Q 3) rearrange Q = It into t = Q/I 1) write ion electron equation & determine mole ratio 2) use mole ratio to determine the no. of coulombs of charge 3) rearrange Q = It to I = Q/t

Nuclear Chemistry Types of Radiation Nuclear Equations Half - lives Artificial radioisotopes - stable nuclei can be made unstable by bombarding them with particles such as protons, neutrons or alpha particles. these radioisotopes usually have short half-lives Uses Fission: nuclei of heavy element bombarded with neutrons causes it to split into lighter nuclei, neutrons, energy, 2 neutrons released bombard other nuclei - self-sustaining (chain reaction isotopes - atoms of the same element with differing mass no.'s & therefore different no.'s of neutrons Radioisotopes - unstable nuclei which emit radiation & energy to form stable nuclei Background Radiation Alpha Beta Gamma stability depends on proton:neutron ratio stable nuclei (lighter elements) contain a roughly equal no. of neutrons & protons as the nuclei of the elements increase in size, the ratio of neutrons:protons increases nuclei of heavier atoms are therefore unstable, most of the isotopes of elements beyond element 83 are unstable radioactivity is the result of unstable nuclei rearranging to from stable nuclei the world contains many radioactive sources - background radiation this ranges from, rocks, building materials, cosmic rays, medical applications, disposal of nuclear waste, smoke detectors helium atom (^4v2He), can't get through paper positive charge, strongly deflected by a positive charge produced when a neutron breaks down to produce a proton & an electron, the proton stays in the nucleus, the electron (^-1v0e) (beta particle) is emitted can't get through aluminium negative charge, slightly deflected by a positive charge high energy electromagnetic wave can't get through lead no charge, therefore no deflection Alpha Beta mass number decreases by 4 atomic number decreases by 2 atomic number decreases by one the half-life of a radioisotope is the time taken for the activity or mass of a sample to halve not effected by temperature or pressure or chemical states different radioisotopes of the same element have different half-lives e.g. lead-212 has a half-life of 10.6 while lead-214 has a half-life of 26.8 minutes half-life & radiation intensity are different, the half-life is for a particular isotope & the intensity for the mass or concentration of a isotope present the symbol given to half-life is t1/2 the decay of individual nuclei within a radioisotope is random, the decay curves for all isotopes all follow the same pattern medicine scientific research industry cobalt-60, cancer treatment if used in the body, radioisotopes should have short half-lives & be beta or gamma because alpha particles cause cellular damage carbon dating during photosynthesis, plants take in carbon-14 s part of their CO2, when a plant dies there is no more uptake of CO2 & therefore the carbon-14 in the plant decays, the proportion of carbon-14 to carbon-12 changes so the age can be measured by this, the half-life of carbon-14 is 5730yrs measuring thickness of thin metals (alpha) Fusion: heavy nuclei are formed by the fusing of 2 light nuclei - takes place in stars

Unit 3 - Chemical Reactions