Question

Oxidation of \(\mathrm{SO}_{2}\) to \(\mathrm{SO}_{3}\) by \(\mathrm{O}_{2}\) is an cxothermic reaction. The yicld of \(\mathrm{SO}_{3}\) will be maximum when(1) Temperature is increased and pressure is kept constant. (2) Temperature is reduced and pressure is increased. (3) Both temperature and pressure are increased. (4) Both temperature and pressure are reduced.

Short answer

Option 2: Temperature is reduced and pressure is increased.

Step-by-step solution

Understand the Reaction

The oxidation of \(\text{SO}_2\) to \(\text{SO}_3\) by \(\text{O}_2\) is expressed by the following exothermic reaction equation: 2\(\text{SO}_2 + \text{O}_2} \rightarrow 2\text{SO}_3 \). In this reaction, heat is released.

Consider Le Chatelier's Principle

Le Chatelier's Principle states that if a system at equilibrium is disturbed, the system will adjust itself to counteract the disturbance and restore a new equilibrium. An exothermic reaction will shift towards the reactants if the temperature is increased. Hence, lower temperatures favor the formation of products.

Analyze the Effect of Pressure

The reaction involves a decrease in the number of moles of gas (3 moles of gas reactants to 2 moles of gas products). According to Le Chatelier's Principle, increasing pressure will shift the equilibrium towards the side with fewer moles of gas, favoring the formation of \(\text{SO}_3\).

Determine the Optimal Conditions

To maximize the yield of \(\text{SO}_3\), we need conditions that favor the formation of the product. Therefore, a decrease in temperature and an increase in pressure will maximize the yield of \(\text{SO}_3\). Based on the given options, the correct answer is option 2.

Key concepts

Oxidation Reaction

Oxidation reactions involve the transfer of electrons between substances. In the reaction we are studying, sulfur dioxide (SO₂) is oxidized to sulfur trioxide (SO₃). The simplified reaction is represented as:

2SO₂ + O₂ → 2SO₃

In this process, sulfur (in SO₂) increases its oxidation state from +4 to +6 in SO₃. For oxidation reactions, the substance that gains oxygen or loses electrons is oxidized, while the substance that loses oxygen or gains electrons is reduced. Here, SO₂ is oxidized to SO₃, and O₂ is reduced.

Exothermic Reaction

An exothermic reaction is one that releases heat into the surroundings. The oxidation of SO₂ to SO₃ is an exothermic reaction. During the reaction, energy is released which often makes the surrounding environment feel warmer.

One important characteristic of exothermic reactions is that they tend to have lower energy products compared to the reactants. This energy difference is released as heat. The reaction can be presented in the form:

2SO₂ + O₂ → 2SO₃ + heat

Because heat is released, this favors lower temperatures for product formation according to Le Chatelier's Principle.

Equilibrium Shift

Equilibrium in a chemical reaction occurs when the rate of the forward reaction equals the rate of the reverse reaction. The reaction of SO₂ to SO₃ reaches equilibrium when the concentrations of reactants and products remain constant over time.

According to Le Chatelier's Principle, changes in conditions (like temperature or pressure) can disturb the equilibrium and cause the system to adjust.

• Temperature: For the exothermic oxidation of SO₂, increasing temperature will shift the equilibrium towards the reactants (SO₂ and O₂). Decreasing temperature favors the formation of the product SO₃.
• Pressure: The reaction involves a decrease in the number of gas molecules (from 3 moles to 2 moles). Increasing the pressure shifts the equilibrium towards the side with fewer gas molecules, favoring the formation of SO₃.

Thus, to maximize SO₃ yield, lower the temperature and increase the pressure.