Question

Which of the following statements is correct about $\text{O}_2$ and $\text{O}_3$ molecule?

• A. $\text{O}_2$ and $\text{O}_3$ are paramagnetic
• B. The enthalpy change during the formation of $\text{O}_3$ from $\text{O}_2$ is positive
• C. The entropy change in the formation of $\text{O}_3$ from $\text{O}_2$ is positive
• D. $\text{O}_3$ is more stable than $\text{O}_2$

Hint:

Ozone formation requires energy (like UV light), so it is endothermic (+$\Delta H$).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Ozone ($\text{O}_3$) is an allotropic form of oxygen ($\text{O}_2$). Its formation is a non-spontaneous, endothermic process.
Step 2: Key Formula or Approach:
$3\text{O}_2 \rightarrow 2\text{O}_3$, $\Delta \text{H} = +284.5\text{ kJ/mol}$.
Step 3: Detailed Explanation:
- (A) $\text{O}_2$ is paramagnetic (unpaired electrons), but $\text{O}_3$ is diamagnetic.
- (B) Formation of ozone is endothermic, so $\Delta \text{H}$ is positive.
- (C) 3 moles of gas yield 2 moles of gas, so entropy decreases ($\Delta \text{S}$ is negative).
- (D) Since $\Delta \text{H}>0$ and $\Delta \text{S}<0$, $\Delta \text{G}$ is positive at all temperatures. Ozone is unstable and spontaneously decomposes back to $\text{O}_2$.
Step 4: Final Answer:
Statement (B) is correct.