Topic 8 - Sulphur and the Contact Process

Flashcards covering the raw materials, chemical equations, specific reaction conditions, equilibrium effects, and safety procedures for the Contact process.

What are the raw materials used in the industrial manufacture of sulphuric acid ($H_2SO_4$)?

Sulfur (mined from deposits or recovered from fossil fuel impurities during desulfurization) and oxygen (obtained from the fractional distillation of liquefied air).

What chemical equation represents the burning of sulfur in oxygen during Step 1 of the Contact process?

$$S_{(s)} + O_{2(g)} \rightarrow SO_{2(g)}$$

What chemical equation represents the roasting of zinc blende in oxygen during Step 1 of the Contact process?

$$2ZnS_{(s)} + 3O_{2(g)} \rightarrow 2ZnO_{(s)} + 2SO_{2(g)}$$

What is the reversible chemical equation for the formation of sulfur trioxide in Step 2 of the Contact process?

$$2SO_{2(g)} + O_{2(g)} \rightleftharpoons 2SO_{3(g)}$$

What reaction conditions are required in Step 2 of the Contact process?

A temperature of $450\text{ }^\text{o}\text{C}$, a pressure of $2\text{ }\text{atm}$ ($200\text{ }\text{kPa}$), and a Vanadium (V) oxide catalyst ($V_2O_5$).

Why is sulfur trioxide ($SO_3$) not dissolved directly in water to make sulphuric acid?

The reaction of $SO_3$ with water is highly exothermic and causes a dangerous acid mist to form.

What chemical equation describes the formation of oleum (fuming sulphuric acid) in Step 3?

$$SO_{3(g)} + H_2SO_{4(l)} \rightarrow H_2S_2O_{7(l)}$$

What chemical equation represents the reaction of oleum with water to produce sulphuric acid of required concentration?

$$H_2S_2O_{7(l)} + H_2O_{(l)} \rightarrow 2H_2SO_{4(l)}$$

Why must oleum always be added to water rather than adding water to oleum?

The reaction is highly exothermic, so adding water to oleum could cause the acid to spit out of the container and produce severe burns.

How does decreasing temperature affect the rate and yield of the reaction $2SO_{2(g)} + O_{2(g)} \rightleftharpoons 2SO_{3(g)} + \text{Energy}$?

Decreasing temperature favours the exothermic reaction, shifting equilibrium to the right to produce a higher percentage yield, but it slows down the rate of reaction.

What are the effects and drawbacks of increasing pressure in the reaction $2SO_{2(g)} + O_{2(g)} \rightleftharpoons 2SO_{3(g)}$?

Increasing pressure shifts equilibrium to the right (fewer gaseous moles) to give a higher percentage yield and faster rate, but high pressure equipment is expensive and carries a high risk of explosion.

What is the effect of the Vanadium (V) oxide catalyst ($V_2O_5$) on the reaction yield and rate?

It results in a faster reaction rate, but it has no effect on the equilibrium yield.