Concentration Consideration

Concentration plays a vital role in any reaction. Every reaction proceeds at a pace that is dictated by the concentration of the reactants. The profitability and viability of a reaction also depend on the concentration of the product generated as a result of the reaction.

Therefore when a reaction has to be done at a large scale, the concentrations of the reactants and the final product play a very important role. Without concentration considerations, industries would have no way to tell if the reaction they are doing will bring them profit or not.

What is Concentration?

Concentration refers to the amount of a specific entity present in a given region. This amount can be expressed in various terms like moles, kilograms, etc. The concentration of an entity is usually talked about with reference to a solution or mixture of some kind. In terms of reactions, when the concentration of reactants is spoken about, it refers to the concentration of reactants in the reactant mixture.

Le Chatelier’s principle for concentration

The importance of concentration consideration cannot be expressed properly without considering its effect on any equilibrium. All reactions occur to reach an equilibrium, but most industries undertake certain practices to tip the equilibrium in their favour. To make this happen, Le Chatelier’s principle is used in conjugation with the concentration of the reactants.

Every reaction can be understood in terms of the number of moles of an entity. When we say A + B → C, here we refer to the concentrations as 1 mole of A reacts with 1 mole of B to produce 1 mole of C. If this reaction were to come to an equilibrium, an equal amount of product would break down to produce the reactant compared to the amount of reactant that would be consumed to create the product.

To tip this equilibrium to produce more product, the concentration of the reactants in the reactant mixture would have to be changed. According to Le Chatelier’s principle, when the number of moles of reactants is greater than the number of moles of product, then increasing the number of moles of reactants will yield more product. This happens because, at equilibrium, the pressure of the reactant and the product mixtures becomes constant. But adding more reactants to the reactant mixture will increase its pressure compared to the product mixture. Therefore, to stabilise the pressures, more products will be produced, and thus the equilibrium will move in the forward direction.

The converse of this consideration is that if fewer moles of reactants produce a greater number of moles of product, increasing the concentration of the reactants will decrease the amount of product produced. To make a reaction profitable, concentration considerations are undertaken in accordance with Le Chatelier’s principle; this gives industries an accurate estimation of the changes needed to yield a profitable reaction.

What is Concentration Consideration?

One of the most prominent examples of concentration consideration in the industries is found in the contact process. The second step in the contact process is the conversion of sulphur dioxide into sulphur trioxide.

After the product of sulphur dioxide is in the contact process, sulphur trioxide is generated from sulphur dioxide. This reaction is important since sulphur trioxide is the starting material to form oleum from which sulphuric acid can be produced.

Due to the importance of this step, it is imperative that the yield of sulphur trioxide is maximised as much as possible. In order to do this, various factors like temperature, pressure, and concentration of the reactants come into play. Therefore, the concentration of the reactants is very important since it has a say in the total amount of sulphur trioxide that will be produced.

The reaction of sulphur dioxide converting to sulphur trioxide is given as

2SO2 + O2 ⇒ 2SO3

According to Le Chatelier’s principle, if the number of moles of reactants on the left side of the equilibrium is increased, the number of moles of products formed on the right side will also increase. That is, the equilibrium will be pushed towards the product side.

However, this brings us to a dilemma regarding an economical solution. The amount of sulphur dioxide produced depends on the first step of the contact process. For example, the amount of sulphur dioxide can be increased by roasting more metal sulphide or burning more sulphur, neither of which can be increased beyond a certain mandated amount.

Therefore the economical solution would be to increase the oxygen concentration in the reactants side. Increasing the concentration of oxygen is easier as oxygen is available in the air, and passing more air would automatically increase oxygen concentration.

Increasing the concentration of oxygen will lead to a higher amount of sulphur dioxide getting converted. But at the same time, the gas that is passed over the catalyst vanadium pentoxide will have more oxygen which has nothing to react with.

This means that even with a higher amount of sulphur dioxide converted, the amount of sulphur trioxide being produced every day will be less since the concentration of sulphur dioxide in the reactant mixture will not be enough for the catalyst to make the conversion.

Conclusion

The reactant ratio of 1:1 yields the highest amount of sulphur trioxide since it finds a fair balance between converting sulphur dioxide using oxygen and allowing the catalyst to shift the reaction to the right side of the equilibrium.

Producing sulphuric acid is a very important task, and the concentration of each reactant plays an important role in this. Therefore it is imperative that the concentration considerations in the contact process be focused upon when preparing to manufacture sulphuric acid.