Learning Objectives https://www.youtube.com/watch?v=xjLUJ-7m5v8 understand the role of sulphuric acid as an acid and as an oxidising agent recall at least one process for the manufacture of sulphuric acid in terms of an equilibrium process and its major uses as an industrial chemical understand the environmental impact of sulphuric acid manufacture evaluate ways of minimising these environmental impacts Contact Process Fuse School (5 min) https://www.youtube.com/watch?v=xjLUJ-7m5v8

World Production of Sulfuric Acid

Sulphur is a waste product and VERY cheap

The contact process H2SO4 manufacture Or PbS or FeS2 or other sulfur ores 4 FeS2(l) + 11O2(g)  Fe2O3(s) + 8SO2(g) 2 PbS(l) + 3O2(g)  2 PbO(s) + 2SO2(g) Sulphur is so cheap why bother with this process!!! Iron(II)sulfide (pyrite), fools gold S8 Sulphur is burnt in air S(l) + O2(g)  SO2(g)

EQUILIBRIUM: 2nd Reaction Reaction Summary Rx 1: S(l) + O2(g)  SO2(g) V2O5 Rx 2: 2SO2(g) + O2(g) 2SO3(g) ∆H = -196 KJ/mol This reaction is the only one of the 3 processes we can change because it us in equilibrium, as we did with the Haber process.

FACTORS AFFECTING THE POSITION OF EQUILIBRIUM CONCENTRATION SUMMARY Le Chatelier 2SO2(g) + O2(g) 2SO3(g) + Energy INCREASE CONCENTRATION OF A REACTANT EQUILIBRIUM MOVES TO THE RIGHT THE EFFECT OF CHANGING THE CONCENTRATION ON THE POSITION OF EQUILIBRIUM DECREASE CONCENTRATION OF A REACTANT EQUILIBRIUM MOVES TO THE LEFT INCREASE CONCENTRATION OF A PRODUCT DECREASE CONCENTRATION OF A PRODUCT Predict the effect of increasing the concentration of O2 on the equilibrium position 2SO2(g) + O2(g) 2SO3(g) EQUILIBRIUM MOVES TO RHS Predict the effect of decreasing the concentration of SO3 on the equilibrium position EQUILIBRIUM MOVES TO RHS

AFFECTING THE POSITION OF EQUILIBRIUM Le Chatelier PRESSURE When studying pressure changes, we consider the number of gaseous molecules only. INCREASE PRESSURE MOVES TO THE SIDE WITH FEWER GASEOUS MOLECULES DECREASE PRESSURE MOVES TO THE SIDE WITH MORE GASEOUS MOLECULES THE EFFECT OF PRESSURE ON THE POSITION OF EQUILIBRIUM Predict the effect of an increase of pressure on the equilibrium position of.. 2SO2(g) + O2(g) 2SO3(g) MOVES TO RHS :- fewer gaseous molecules H2(g) + CO2(g) CO(g) + H2O(g) NO CHANGE:- equal numbers on both sides

AFFECTING THE POSITION OF EQUILIBRIUM Le Chatelier TEMPERATURE • temperature is the only thing that can change the value of the equilibrium constant. • altering the temperature affects the rate of BOTH backward and forward reactions • the direction of movement depends on the sign of the enthalpy change. REACTION TYPE DH INCREASE TEMP DECREASE TEMP EXOTHERMIC - TO THE LEFT TO THE RIGHT ENDOTHERMIC + Predict the effect of a temperature increase on the equilibrium position of... 2SO2(g) + O2(g) 2SO3(g) DH = - ve moves to the LHS

FACTORS AFFECTING THE POSITION OF EQUILIBRIUM CATALYSTS Adding a catalyst DOES NOT AFFECT THE POSITION OF EQUILIBRIUM. However, it does increase the rate of attainment of equilibrium. This is especially important in reversible, exothermic industrial reactions such as the Haber or Contact Processes where economic factors are paramount. Vanadium(v) oxide catalyst used for the manufacture of sulfuric acid.  The gas inlet duct can be seen in the middle of the picture.

Compromise BUT Low temps mean low reaction rates, so we may get a higher yield but it will take a long time to get it. Not good for business. A compromise temp, as well as the use of a catalyst will aid in speeding up the reaction to a more acceptable standard. Temp between 700 K (425 0C) (this gives fast rate) Overall conversion is 90% to SO3

More money, more SO3, but not worth it… Also a high pressure would favour, using Le Chatelier's Principle, the formation of SO3 in the 2nd step, however its too expensive. Reactants are compressed to 2 atm to achieve the desired flow rate in the reactor, but it is for forcing the gases more than Le Chatelier's Principle effects. Pure O2 would drive the equilibrium to the right, however its an unnecessary expense. And there is no room on the catalyst for all that extra O2, so not enough SO3 for it to react there anyway Low temperatures, because its exothermic, would be best for Le Chatelier's Principle, but it slows the rate too much. Addendum: Metal corrosion is a big issue in the manufacture of sulfuric acid. Special alloy metals must be used to guard against excessive corrosion. Nickel, chromium, molybdenum, copper, an silicon are the most important elements that enhance corrosion resistance of alloys.

The contact process LAST STEP Problem is that not only is it slow the reaction is violent exothermic reaction and produces a fog or mist of sulfuric acid that cannot be condensed. In practice the SO3(g) is dissolved in concentrated sulphuric acid (that contains relatively no water) Sulphur trioxide, from the first step, reacts with water to form sulphuric acid (in a mixture of 98% sulphuric acid and 2% water) SO3(g) + H2O(l) H2SO4(l) (Slow and dangerous) SO3(g) + H2SO4(l)  H2S2O7(l) disulphuric acid or oleum H2S2O7(l) + H2O(l)  2 H2SO4(l)

All 3 Reactions: Summary Reaction Summary Rx 1: S(l) + O2(g)  SO2(g) What can we do here? Answer: nothing, it goes 100% V2O5 Rx 2: 2SO2(g) + O2(g) 2SO3(g) ∆H = -196 KJ/mol Here is only place we can manipulate reaction, le Chatelier Rx 3: ACID TOWER Dangerous part of reaction as it is VERY exothermic. BOOM. H2S2O7 called pyrosulfuric acid, why? a)SO3(g) + H2SO4(l)  H2S2O7(l) (disulphuric acid/oleum) (CORROSIVE) b)H2S2O7 + H2O  2H2SO4 Waste gases need to be neutralized by?? Answer : Bases like Na2CO3 SO3 H2SO4

Waste Management and Environmental Impact All three processes are exothermic, meaning energy is produced. This energy is used to generate its electricity or as a source to produce other chemicals. Environmental Impact The chimneys of these plants do leak out some acid that contributes to localized acid rain. However, today they use scrubbers in the chimneys to get rid of the acid rain problem. Can you guess what chemical is sprayed inside the chimney to reduce the acid? Answer: Na2CO3 or other BASES.

The sulphuric acid industry fertilisers electrochemistry – batteries

Uses of sulphuric acid Making fertilisers (phosphate is part of NPK) Ca3(PO4)2(s) 3H2SO4(aq)  3CaSO4(s) 2H3PO4(aq) for N, P, K Phosphate ore And H2SO4(aq + 2 NH3  (NH4)2NO3 Making fertilisers (phosphate is part of NPK)

Uses of sulphuric acid Acids clean metals

Sulfur Uses: Preservatives Preservatives can be categorized into three general types: antimicrobials that inhibit growth of bacteria, yeasts, or molds. Sulfur Dioxide has been used in winemaking since the Romans discovered that if you burn candles made of sulfur inside empty barrels it would prevent them smelling like vinegar. Sulfur dioxide serves all three types, which is one reason why it and related compounds called sulfites are found in so many household products.