AQA A-level physical chemistry chemical equilibrium/ equlibria + Le chateliers principle

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product, the equilibrium tries to remove the extra product - this makes the reverse reaction. go faster so the equilibrium snifts to the left. changing pressure Only affects equilibria involving gases Increasing the pressure shifts the equilibrium to the side with fewer gas molecules. Decreasing the pressure shifts the equilibrium to the side with more gas molecules Changing temperture Increasing the temperture shifts the equilibrium in the endothermic (positive AH) direction to absorb the heat added Deacreasing the temperture shifts the equilibrium in the exothermic (negative AH) direction to replace the heat removed If the forward reaction's endothermic, the reverse reaction will be exothermic following equilibrium reactions the reaction of [Cult₂016] ² with concentrated hydrochloric acid (HCI) is a reaction that follows the equilibrium shift when [Cult₂016] reacts with hydrochloric acid, a copper chloride complex [cucly]² forms [cul1₂016] ² (aq) + 4C\¯ ragi blue copper aqua complex [Cucly] ² (aq) + 6H₂0 (1) green-yellow copper Chloride complex reaction so at any point there will be a mixture of [Cu(H₂016] ²* and [Cucly]²" present in the This reaction is a reversible reaction Container [Cu(H₂0)]²+ is a light blue colour, while [Cucly] ² is a green-yellow you can therefore monitor the equilibrium position this reaction by noting what colour the soloution is if the soloution is blue then the position of equilibrium must lie to the left and there'll be more reactants than products If the soloution is greeny-yellow the equilibrium position must lie to the right and there'll be more of the products I changing the concentration 2+ If you have a test tube containing [Cu(H₂016]²+ you'll see it's a light blue colour If you add concentrated HCl, you'll notice the soloution turn from light blue to a bluey-green as the equilibrium Is established The more HCl you add, the more green the soloution goes as more and more of the [Cucly]²" complex forms This is because by adding HCl, you're increasing the concentration of Cl- in the soloution The equilibrium snifts to the right to try and remove the excess C1- ions from the soloution, and more greeny- yellow [Cucly] forms you can push the equilibrium back to the right by adding distilled water to the reaction container The equilibrium position moves to try and mop up all the extra H₂O molecules you're adding to the soloution by forming more [Cu(H₂016] which turns the soloution blue again changing the temperature The forward reaction of the equilibrium is endothermic (takes in heat) so if you heat the sample containing an equilibrium mixture of [Cu(H₂0)]²+ and [Culci)y]² the equilibrium will move to the right to try and absorb the extra neat This means more of the product forms, and you'll see the solution turn green as more = [Culci)y] ² is is made The opposite happens if you cool the mixture down The reverse reaction is exothermic, the equilibrium will move to the left to favour the reverse reaction to try and make up for the loss of heat • [Cu(H₂015] 2+ complex will form, and the solution will turn more blue This means more of the industrial processes Compromise conditions in industry Ammonia, NH3 used to make fertilisers like ammonium nitrate, ammonium sulfate, and urea and used to make synthetic fibres lincluding. nylon), dyes, explosives and plastics like polyethane + = N₂ 191 + 3H₂(g) 2NH3 (9) AH = -92 kjmol-¹ The percentage of ammonia obtained at equilibrium depends on temperature and pressure low temperatures and nign pressure would give close to 100% conversion whereas low pressure and nigh temperature would give almost no ammonia Almost an ammonia is made by the harber process in which the reaction above is the key step The raw materials for the harber process are air (which provides the nitrogen), water and natural gas (methane, CH₂) These provide the Hydrogen: CH4 (g) + H₂O1g1 CD (g) + 3 H₂ cg1. The nitrogen and hydrogen are fed into a converter in the ratio 1:3 and passed over an iron catalyst Nitrogen and hydrogen flow continously over the catalyst so the gases do not spend long enough in contact with the catalyst to reach equilibrium. There is about 15%. Conversion to ammonia. The ammonia is cooled so that it becomes liquid and is piped off. Any Nitrogen and hydrogen that is not converted into ammonia is fed back into the reactor The catalyst is iron in pea-Sized lumps to increase the surface area). It lasts 5 years before it becomes poisoned by impurities in the gas stream and has to be replaced Ethanol, C₂H₂OH Ethanol is the alcohol in alcoholic drinks produced by fermentation from sugars such as glucose using the enzyme in yeast as a catalyst C6H1₂O6 (aq) →2C₂Hs OH lagi + 2C0₂. cg) Ethanal has many industrial uses: making cosmetics, drugs, detergents, inks and as a motor fuel The main source of ethanal for industrial use is ethene from crude oil. This is obtained by fractional distilation and then cracking C₂ Hy(g) + H₂O rg1=C₂ H₂ OH cg₁ AH=-46 kmol-¹ Ethanal is made by the hydration to ethene The reaction is reversible pressure of 60-70 atm. temperature of 300°C phosphoric acid catalyst The reactants and products are all gaseous at the temperature used. Because it's an exothermic reaction, lower temperatures favour the forward reaction - more ethene and steam are converted to ethanol and you get a better yield but lower temperatures mean a slower rate of reaction SD 300°C is a compromise between maximum yied and a faster reaction. Higner pressure favours the forward reaction since it moves to the side with fewer molecules of gas increasing the pressure also increases the rate of reaction. but high pressures are expensive to produce - you need stronger pipes containers to withstand the high pressure So the 60-70 atm is a compromise between maximum yield and minimum expense only a small proportion of the ethene reacts each time the gases pass through the reactor. To save money and raw materials. the unreacted ethene is seperated from the ethanol and recycled back into the reactor. Thanks to this 95% of the ethene is eventually converted to ethanol Methanol, CH₂OH methanol is used principally as a chemical feedstock - a starting material for making other chemicals. In particular it's used to manufacture methanal (formaldehyde) which is used to make plastics such as bakelite. Methanol is also used in the manufacture of other Plastics such as terglene and perspex. Methanol may also be used (alone or added to petrol) as a motor fuel e Corgs + 2H₂(g) CH3OH (9) AH =-91 x) mol-¹ pressure of 50-100atm. temperature of 250°℃ a catalyst of a mixture of Copper, zinc oxide and aliminium oxide the starting gas mixture is called synthesis gas and is made by reacting methane or Propane with steam highest yield at low temperatures and nigh pressure las is the case for the ethanol synthesis reaction) compromise conditions are used. 5-10%. yield is produced