Contact Process

Question 1

contact process

Answer 1

used to make sulfuric acid

Question 2

stage 1

Answer 2

sulfur burns in air to produce sulfur dioxide

sulfur + oxygen → sulfur dioxide
S (s) + O2 (g) → SO2 (g)

Question 3

stage 2

Answer 3

sulfur dioxide and oxygen react together to produce sulfur trioxide

sulfur dioxide + oxygen ⇌ sulfur trioxide
2SO2 (g) + O2 (g) ⇌ 2SO3 (g)

Question 4

stage 3

Answer 4

sulfur trioxide is converted to sulfuric acid

sulfur trioxide + water → sulfuric acid
SO3 (g) + H2O (l) → H2SO4 (aq)

Question 5

temperature chosen to make sulfur trioxide ( step 2)

Answer 5

450°C

forward reaction is exothermic
backward reaction is endothermic
temperature increased - equilibrium position moves to the left and equilibrium yield of sulfur trioxide decreases
low temperature favours a high equilibrium yield

Question 6

why is temperature chosen a compromise?

Answer 6

low enough yo achieve a reasonable equilibrium yield but high enough to achieve a reasonable rate of reaction 
also vanadium(V) oxide catalyst only works above 380°C

Question 7

pressure chosen to make sulfur trioxide (stage 2)

Answer 7

2 atmospheres (200 kPa)
in balanced equation - 3 mol of gas on there left but only 2 mol of gas on the right
if pressure is increased - equilibrium position moves to the right and the equilibrium yield of sulfur trioxide increases
however in this reaction - equilibrium position is already far to the right so no need for high pressures
2 atm just enough to push the gases through the converter

Question 8

catalyst chosen to make sulfur trioxide (stage 2)

Answer 8

vanadium(V) catalyst, V2O5

does NOT change the position of the equilibrium