topic 5 - the haber process, industry and fuel cells Flashcards
the haber process
produces ammonia
nitrogen + hydrogen ⇌ ammonia (+heat)`
N2 + 3H2 ⇌ 2NH3
conditions for the haber process
450°C
200 atm
iron catalyst
why is the pressure in the haber process 200atm
as pressure is increased, equilibrium favours the side with fewer moles of gas in order to reduce pressure
higher pressures favour the forward reaction (4 moles to 2)
pressure is therefore set as high as possible to give the best yield without making the plant too expensive to build
why is the temperature in the haber process 450°C
if the temperature is decreased, equilibrium favours the exothermic reaction to produce more heat
the forward reaction in the Haber process is exothermic so increasing temperature moves equilibrium the wrong way
lower temperatures mean a lower rate of reaction, which is undesirable in industry
450°C is a compromise between maximum yield and speed of reaction
why is an iron catalyst used in the haber process
the catalyst speeds up the reaction so it reaches equilibrium faster
without the catalyst, the process would need to be carried out at an even higher temperature in order to get a quick enough reaction but that would decreased percentage yield further
CATALYST HAS NO IMPACT ON % YIELD OR POSITION OF EQUILIBRIUM
4 changes in factors affecting attainment of equilibrium
INCREASE in temperature, increases rate of reaction, increases rate at which you reach equilibrium
INCREASE in pressure, increases rate of reaction, increases rate at which you reach equilibrium
INCREASE in concentration, increases rate of reaction, increases rate at which you reach equilibrium
having a CATALYST present, increases rate of reaction, increases rate at which you reach equilibrium
the cost of what two things affect choices in industry
cost of extracting and acquiring raw materials
energy costs
why do we control the conditions of an equilibrium reaction
controlling temperature, pressure and the presence of a catalyst maximises yield but keeps the reaction running at an acceptable rate
explain the cost of extracting and acquiring raw materials as affecting choices in industry
extracting and acquiring raw materials will affect whether the process is economically viable
if they are too expensive, making the product may not be profitable
explain the cost of energy as affecting choices in industry
generally high pressures and temperatures cost more to maintain so lower temperatures or pressure are preferred and used wherever possible
what do plants need
plants need enough nitrogen, phosphorus and potassium for their growth and life processes
fertilisers provide these elements, helping them to increase crop yield because crops can grow faster and bigger
why are ammonia fertilisers good (3)
- you can control how much is made
- you can control the chemical composition of them
- they are soluble so all chemicals dissolve down into the soil to reach the plants
what are the reactions needed to make fertilisers
ammonia can be reacted with oxygen and water to make nitric acid
ammonia reacts with the acids to make ammonium salts (ammonium nitrate)
NH3 + HNO3 -> NH4NO3
how would you prepare ammonium sulfate in a LAB (5)
1) add a few drops of methyl orange to ammonia
2) add dilute sulfuric acid slowly using a burette until yellow colour turns red, swirling the flask as acid is added
3) the colour change means that all of the ammonia has been neutralised
4) this solution of ammonia is impure so note how much acid was added and repeat the titration without the indicator
5) the solution should then be evaporated until a little bit is left and can be left to crystallise, filtered and dried
why can lab preparation not be scaled up easily for industry
crystallisation is too slow for industry
steam baths and burettes are impractical for large quantities
