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Chapter 22: Problem 63

Describe the contact process for the production of sulfuric acid.

Short Answer

Expert verified
In the contact process, sulfur dioxide is first produced by burning sulfur or iron pyrites in oxygen. This sulfur dioxide is then converted into sulfur trioxide using a catalyst of vanadium(V) oxide. Finally, the sulfur trioxide is absorbed in sulfuric acid to produce fuming sulfuric acid (oleum) which is then diluted with water to give concentrated sulfuric acid.

Step by step solution

01

Sulphur Dioxide Production

Firstly, sulfur or iron pyrites (iron(II) sulfide) is burned in oxygen to produce sulfur dioxide. The reactions can be shown as: \(S(s) + O2(g) \rightarrow SO2(g)\) for sulfur, and \(4FeS2(s) + 11O2(g) \rightarrow 2Fe2O3(s) + 8SO2(g)\) for iron pyrites.
02

Conversion to Sulphur Trioxide

The sulfur dioxide is then converted into sulfur trioxide using a catalyst in the form of vanadium(V) oxide. The reaction is reversible, making it vital to ensure the reaction conditions are precisely maintained to produce the highest possible yield of sulfur trioxide. The reaction can be shown as: \(2SO2(g) + O2(g) \rightleftharpoons 2SO3(g)\)
03

Producing Sulfuric Acid

The sulfur trioxide is first absorbed in concentrated sulfuric acid to give fuming sulfuric acid also known as oleum. The fuming sulfuric acid can be diluted with water to give concentrated sulfuric acid. So the overall reaction can be shown as: \(SO3(g) + H2SO4(l) \rightarrow H2S2O7(l) \rightarrow H2SO4(l) + H2O(l)\)

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Sulfur Dioxide Production
Understanding the first stage of the contact process begins with the production of sulfur dioxide. In simple terms, sulfur or an alternative source like iron pyrites (which contains sulfur) is burned in the presence of oxygen. During this reaction, the sulfur (S) combines with oxygen (O2) to form sulfur dioxide (SO2). The equations representing these reactions are:

For sulfur: \[S(s) + O_2(g) \rightarrow SO_2(g)\]
And for iron pyrites: \[4FeS_2(s) + 11O_2(g) \rightarrow 2Fe_2O_3(s) + 8SO_2(g)\]

It is essential to carry out this step carefully, as the purity of the sulfur dioxide gas significantly affects the effectiveness of the subsequent steps in the contact process.
Conversion to Sulfur Trioxide
Once sulfur dioxide is obtained, the next phase involves its conversion to sulfur trioxide (SO3). This is achieved with the help of a catalyst that accelerates the reaction without being consumed by it.

The reaction for forming sulfur trioxide is as follows: \[2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)\]

This reaction is reversible, indicating a state of equilibrium between reactants and products. Factors such as temperature, pressure, and the presence of a catalyst are critical in driving the reaction towards the production of sulfur trioxide while maximizing yield.
Catalyst Vanadium(V) Oxide
The role of vanadium(V) oxide in the contact process cannot be overstated. Acting as a catalyst, vanadium(V) oxide (V2O5) significantly enhances the rate at which sulfur dioxide is converted to sulfur trioxide. Catalysts are crucial in industrial chemical processes as they reduce energy costs by requiring lower temperatures and pressures without undergoing permanent change themselves.

Catalysts also ensure that reactions are more efficient and environmentally friendly by minimizing waste. Vanadium(V) oxide is particularly effective for this purpose and is a critical component of the contact process.
Fuming Sulfuric Acid
Fuming sulfuric acid, also known as oleum, is an intermediate in the production of sulfuric acid. It is a solution of sulfur trioxide in concentrated sulfuric acid. Oleum is further processed to produce sulfuric acid, which, in this context, is the desired end product. To understand this transformation, one needs to grasp the hydration of oleum as shown in the chemical reaction:

\[SO_3(g) + H_2SO_4(l) \rightarrow H_2S_2O_7(l)\]
\[H_2S_2O_7(l) + H_2O(l) \rightarrow 2H_2SO_4(l)\]

This shows the conversion of sulfur trioxide to sulfuric acid via the intermediate, fuming sulfuric acid.
Chemical Equilibrium
The concept of chemical equilibrium is fundamental to the contact process. The reversible nature of the reaction that converts sulfur dioxide to sulfur trioxide means that it reaches a point where the rate of the forward reaction equals the rate of the backward reaction, and the concentrations of reactants and products remain constant.

It's essential to optimize the conditions to favor the formation of sulfur trioxide, which includes adjusting temperature, pressure, and using a catalyst. Chemical equilibrium is a delicate balance, and understanding it is crucial for any student studying the contact process since it affects the yield and efficiency of the reaction.

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