The Contact process is used in the to produce of sulfuric acid. This Modules describe the factors for the conditions used in the procedure by considering the result of proportions, temperature, pressure and catalyst ~ above the composition of the equilibrium mixture, the rate of the reaction and the economics of the process. The contact Process:

action 1: do sulfur dioxide action 2: transform sulfur dioxide right into sulfur trioxide (the reversible reaction in ~ the heart of the process) step 3: convert sulfur trioxide into concentrated sulfuric acid

Step 2: convert sulfur dioxide into sulfur trioxide

This is a reversible reaction and also exothermic.

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<2SO_2 (g) + O_2(g) ightleftharpoons 2SO_3 (g) ;;; DeltaH=-196; kJ/mol label3>

A circulation sptcouncil.nete for this component of the process looks choose this:


The factors for every these problems will be explored in detail further under the page.

Step 3: convert sulfur trioxide into sulfuric acid

This cannot be done by simply including water come the sulfur trioxide; the reaction is so uncontrollable the it creates a fog that sulfuric acid. Instead, the sulfur trioxide is very first dissolved in concentrated sulfuric acid:

< H_2SO_4 (l) + SO_3(g) ightarrow H_2S_2O_7 (l) label4>

The product is recognized as fuming sulfuric acid or oleum, which can then be reacted safely through water come produce focused sulfuric mountain - double as much originally offered to do the fuming sulfuric acid.

< H_2S_2O_7 (l) + H_2O_(l) ightarrow 2H_2SO_4 (l) label5>

Explaining the conditions

The mixture of sulfur dioxide and oxygen going into the reactor is in same proportions by volume. Avogadro"s regulation says the equal quantities of gases at the same temperature and also pressure contain same numbers that molecules. That method that the gases are going into the reactor in the ratio of 1 molecule the sulfur dioxide come 1 that oxygen.

That is an excess of oxygen relative to the proportions demanded by the equation.

<2SO_2 (g) + O_2(g) ightleftharpoons 2SO_3 (g) ;;; DeltaH=-196;kJ/mol>

According come Le Chatelier"s Principle, raising the concentration of oxygen in the mixture causes the place of equilibrium to transition towards the right. Since the oxygen comes from the air, this is a an extremely cheap method of boosting the conversion of sulfur dioxide right into sulfur trioxide.

Why not use an even higher proportion that oxygen? This is easy to check out if friend take severe case. Suppose you have actually a million molecules of oxygen come every molecule that sulfur dioxide. The equilibrium is going to it is in tipped really strongly in the direction of sulfur trioxide - practically every molecule that sulfur dioxide will certainly be converted into sulfur trioxide. However, you aren"t walk to produce much sulfur trioxide every day. The vast majority of what you space passing end the catalyst is oxygen which has nothing to reaction with.

By raising the ratio of oxygen you deserve to increase the percent of the sulfur dioxide converted, yet at the same time to decrease the total amount of sulfur trioxide made each day. The 1:1 mixture results in the best feasible overall productivity of sulfur trioxide.

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Equilibrium considerations:

< 2SO_2(g) + O_2(g) ightleftharpoons 2SO_3(g) ;;; Delta H = -196;kJ/mol>

Notice that there space three molecules on the left-hand next of the equation, but only 2 on the right. According to Le Châtelier"s Principle, if you rise the pressure the mechanism will respond by donate the reaction which produces fewer molecules. That will reason the pressure to autumn again. To obtain as much sulfur trioxide as possible in the equilibrium mixture, you require as high a push as possible. High pressures also increase the price of the reaction. However, the reaction is excellent at pressures close to atmospheric pressure!

Economic considerations: Even in ~ these relatively low pressures, over there is a 99.5% switch of sulfur dioxide right into sulfur trioxide. The very little improvement that you could accomplish by enhancing the press isn"t precious the expense of producing those high pressures.