Reversible Reactions in Industry

Question 1

in order to maximise profits what are the problems chemists face when converting reactants to products in reversible reactions

Answer 1

• doing it as quickly as possible

- and as completely as possible

Question 2

in the haber process to make ammonia, N2(g) + 3H2(g) = 2NH3(g) with a delta H of -92, what would the ideal temperatures and pressures be in order to maximise the yield of ammonia

Answer 2

• decrease the temperature

- increase the pressure

Question 3

why those conditions

Answer 3

• decreasing temp shifts the equilibrium to the exothermic direction (forwards) making more product
• increasing pressure shifts the equilibrium to the position with fewer moles of gas (forwards)

Question 4

the conditions used in the haber process are 450C an 250atm, giving a yield of just over 30%. what is the overarching reason why lower temperatures arent used

Answer 4

• the rate of reaction would be too low

- to the point where the yield of ammonia for a given time would be less if the temp was decreased any further

Question 5

what is the first problem with having too low temperatures, considering the reactants being used

Answer 5

• the reaction between nitrogen and hydrogen is very slow at lower temps
• especially because of the strong triple bonds between nitrogen atoms
• this produces a high activation energy for the reaction

Question 6

what substance would be used to increase the rate of reaction by decreasing the activation energy required

Answer 6

a catalyst

Question 7

what catalyst is used in industry and why

Answer 7

• iron
• although there are more effective ones like tungsten and platinum
• they are very expensive so iron is used

Question 8

with a catalyst now being used, what is another problem that comes with using low temperatures in the haber process

Answer 8

• catalysts dont function efficiently at low temperatures

- so relatively high temps are necessary for it to work effectively anyway

Question 9

despite high temps having to be used in order for the reaction to smoothly occur, why is it also disadvantageous

Answer 9

• very high temps would be expensive as extra energy costs would have to be paid
• the position of equilibrium would also shift to the left
• causing the yield to decrease

Question 10

what problem do chemists now run into when all of this has been considered

Answer 10

• when they try to change one factor to increase the rate of reaction
• they are changing another factor which decreases the rate of the reaction

Question 11

what therefore has to be made in order to find the balance to maximise yield

Answer 11

a compromise

Question 12

why does a compromise need to be made with the pressure as well despite an increase in pressure
increasing the yield

Answer 12

• because an increase in pressure requires more energy and therefore more money
• and a lower pressure costs less but results in a lower yield

Question 13

how is the efficiency and cost effectiveness of the subsequent reactions increased

Answer 13

• after the nitrogen and hydrogen have been separated from the ammonia
• they are mixed with fresh nitrogen and hydrogen to be fed into the reaction chamber

Question 14

what is the contact process

Answer 14

the manufacturing method for sulfuric acid

Question 15

what is the catalyst in the contact process

Answer 15

vanadium pentoxide (V oxide)

Question 16

what is the equation for this reaction

Answer 16

2SO2 + O2 = 2SO3

Question 17

at 1 atm the yield of SO3 is at 97%, so would it be better for the industry to increase the pressure and why

Answer 17

• it wouldnt
• although increasing the pressure would increase the yield, it is already so high that the difference wouldnt be significant
• especially when considering the cost of increasing the pressure
• in short, it is not cost effective