The oxidation of `SO_2" by "O_2" to "SO_3` is an exothermic reaction. The yield of `SO_3` will be maximum if

Options

A. temperature is increased and pressure is kept constant
B. temperature is reduced and pressure is increased
C. both temperature and pressure are increased
D. both temperature and pressure are reduced

Answer

To determine the conditions under which the yield of sulfur trioxide (SO₃) will be maximized in the exothermic reaction of sulfur dioxide (SO₂) with oxygen (O₂), we can follow these steps:

### Step 1: Write the balanced chemical equation
The balanced equation for the reaction is:
\[ 2 \, \text{SO}_2(g) + \text{O}_2(g) \rightarrow 2 \, \text{SO}_3(g) \]

### Step 2: Identify the nature of the reaction
This reaction is exothermic, meaning it releases heat. In an exothermic reaction, the formation of products is favored at lower temperatures.

### Step 3: Apply Le Chatelier's Principle
According to Le Chatelier's Principle, if a system at equilibrium is subjected to a change in temperature, pressure, or concentration, the system will adjust to counteract that change and restore a new equilibrium.

### Step 4: Consider temperature
Since the reaction is exothermic, lowering the temperature will shift the equilibrium to the right, favoring the formation of SO₃. Therefore, a lower temperature will maximize the yield of SO₃.

### Step 5: Consider pressure
In the balanced equation, we have 2 moles of SO₂ and 1 mole of O₂ on the reactant side (total 3 moles) and 2 moles of SO₃ on the product side. Increasing the pressure will favor the side with fewer moles of gas. Since there are fewer moles of gas on the product side (2 moles of SO₃), increasing the pressure will also shift the equilibrium to the right, favoring the formation of SO₃.

### Conclusion
To maximize the yield of SO₃, the reaction should be conducted at:
- **Low temperature** (to favor the exothermic reaction)
- **High pressure** (to favor the side with fewer moles of gas)

Thus, the conditions for maximum yield of SO₃ are low temperature and high pressure.