Chapter 16

* Method discovered by German chemist Fritz Haber in * A way to take N 2 from the air and turn it into ammonia. * Previously ammonia had been made from imported bat poo! * m/watch?v=tdEE5uvFhOM

* N 2 + 3H 2  2NH 3 * Reversible reaction * Pressure = 200atm * Temp = 450 o C * Ratio of reactants: * 1N 2 : 3H 2 * N comes from the air. * H is made from natural gas. * 15% yield, unreacted reactants are recycled through. * /watch?v=o1_D4FscMnU

* Between 150 – 300 atmospheres * Number of molecules on each side of the reaction: 4 and 2 * The forward reaction is favoured with high pressure. * In equilibriums involving gases, an increase in pressure favours the reaction which produces the smallest number of molecules. * We don’t use higher pressures because of the cost and danger.

* 400 – 500 o C * The forward reaction is exothermic, so a lower temp would favour the forward reaction. * If the temperature is increased further less ammonia will be formed. * However, at a lower temp the reaction rate would be too low. * The temp needs to be low enough to provide a good yield, but high enough to have a decent rate of reaction.

* Compromise conditions: the conditions which produce a reasonable yield. * Temp: 450 o C * Pressure: 200 atm

* The catalyst speeds up the rate of the reaction without being used up in the reaction. * It lowers the activation energy. * It does not increase the yield, only the rate. * Can be used again and again

* ction?quick=128 ction?quick=128 * rProcess.htm rProcess.htm * process-including-simulation-and.html

* Manufacture of sulphuric acid * Three stages * 1. Burning sulphur in air S + O 2 → SO 2 * 2. Making sulphur trioxide 2SO 2 + O 2 ⇌ 2SO 3 * 3. Making sulphuric acid H 2 SO 4 + SO 3 → H 2 S 2 O 7 H 2 S 2 O 7 + H 2 0 → 2H 2 SO 4

* Stage 2 = reversible reaction 2. Making sulphur trioxide 2SO 2 + O 2 ⇌ 2SO kj mol -1 Temperature used : 450 o C – compromise temp Pressure used : 1 – 2 atm Catalyst : Vanadium (V) oxide 99.5% conversion

The uses of sulphuric acid

* Salt is extracted from underground deposits. * The diaphragm cell is used to electrolyse the salt solution. * 3 useful chemicals can be produced: * NaOH(aq) * Cl 2 (g) * H 2 (g) * OYVM

* Anions present: Cl - and OH - * Discharged: Cl - * Cations present: H + and Na + * H + is discharged as it is less reactive than Na + * OH - ions build up. As H + get discharged, equilibrium corrects the changes and more water molecule disassociate into OH - and H + * The diaphragm keeps the Cl - and the NaOH apart, they would react. * The solution coming out is heated and NaCl crystals are collected and reused.

* Soap * Paper * Aluminium * Bleach

* Swimming pools * Water * Bleach * Hydrochloric acid

* Fuel * Hydrogenation of fats, margarine