the contact process Flashcards
(14 cards)
raw materials needed for making sulfuric acid
sulfur
air (source of oxygen)
water
these are used in three stages
stage 1 contact
sulfur burns in air to produce sulfur dioxide
S (s) + 02 (g) –>SO2(g)
stage 2 contact process
The sulfur dioxide and oxygen react together to produce sulfur trioxide
2SO2 (g) + O2 (g)—> 2SO3 (g)
conditions of stage 2 contact
2 atmospheres pressure (200kPa)
temperature of 450 degrees celsius
vanadium oxide catalyst
under these conditions, equilibrium yield of sulfur trioxide is about 96% !! yay
stage 3 contact process
sulfur trioxide is converted into sulfuric acid (reacts with concentrated sulfuric acid to form oleum which reacts with water)
H20 (l) + SO3 (g) —> H2SO4 (aq)
contact process MAIN equation
reversible reaction, forward reaction is exothermic
2SO2 (g) + O2 (g) ⇌ 2SO3 (g)
what factors determine the pressure chosen (contact)
if the pressure is increased, the equilibrium position moves to the right and the equilibrium yield of sulfur trioxide increases
however, in this stage 2 reaction, equilibrium position is already far to the right- no need for high, 2 atmospheres just enough to push gases tru converter
le chateliers principle
when you change conditions (temp, pressure,concentration) equilibrium shifts to oppose that change
effect of temp change (equilibrium)
if the forward reaction is exothermic, lower temp increases equilbrium yield (more product)
if endothermic, higher temp increases equilibrium yield (more product)
effect of pressure change (equilibrium)
increase pressure- equilibrium shifts toward fewer gas molecules
decrease pressure- equilibrium shifts toward more gas molecules
effect of concentration change (equilbrium)
increase reactants- equilbrium shifts toward right- more products
remove products- equilbrium shifts toward right again - to replace them
effect of catalysts (equilbrium)
they dont affect equilibrium position, only help REACH equilibrium faster
what factors determine temp (contact)
forward reaction in stage 2 is exothermic so backward reaction is endothermic
if temp increased, equilbrium position moves to the left and equilbrium yield of sulfur trioxide decreases
high equilibrium yield is favoured by low temp
how are da hazards controlled (contact)
stage 3 reaction is very exothermic
-would produce a hazardous acidic mist so carried out in two steps
- sulfur trioxide is passed through a concentrated sulfuric acid (made previously) to make a compound called oleum (h2s2o7)
- the oleum is then added to water and the reaction makes a larger volume of the concentrated sulfuric acid
H2S2O7 (l) + H2O (l) —> 2H2SO4 (aq)
