Question:
Which of the following reactions is non-spontaneous?
Which of the following reactions is non-spontaneous?
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Oxidizing power of halogens decreases from \(F_2 > Cl_2 > Br_2 > I_2\).
Updated On: Oct 15, 2026
- \(2F_2 + 2H_2O \rightarrow 4HF + O_2\)
- \(Cl_2 + H_2O \rightarrow HCl + HOCl\)
- \(Br_2 + H_2O \rightarrow HBr + HOBr\)
- \(2I_2 + 2H_2O \rightarrow 4HI + O_2\)
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The Correct Option is D
Solution and Explanation
Concept:
Spontaneity in redox reactions is determined by the standard electrode potential (\(E^{\circ}\)). For a reaction to be spontaneous, the overall cell potential (\(E^{\circ}_{cell}\)) must be positive.
Step 1: Evaluate the reaction trends for Halogens.
Fluorine is the strongest oxidizing agent and readily reacts with water: \[ 2F_2 + 2H_2O \rightarrow 4HF + O_2 \text{ (Spontaneous)} \] As we move down the group, oxidizing power decreases. Chlorine and bromine reactions with water are partially spontaneous or require light/conditions, but the reaction of Iodine with water is endergonic.
Step 2: Analyze the reverse reaction.
The reaction \(2I_2 + 2H_2O \rightarrow 4HI + O_2\) is non-spontaneous because \(I_2\) is not a strong enough oxidizing agent to oxidize water to oxygen. In fact, the reverse reaction (oxidation of \(I^-\) by \(O_2\)) is more favorable in acidic conditions. \[ \boxed{2I_2 + 2H_2O \rightarrow 4HI + O_2} \]
Step 1: Evaluate the reaction trends for Halogens.
Fluorine is the strongest oxidizing agent and readily reacts with water: \[ 2F_2 + 2H_2O \rightarrow 4HF + O_2 \text{ (Spontaneous)} \] As we move down the group, oxidizing power decreases. Chlorine and bromine reactions with water are partially spontaneous or require light/conditions, but the reaction of Iodine with water is endergonic.
Step 2: Analyze the reverse reaction.
The reaction \(2I_2 + 2H_2O \rightarrow 4HI + O_2\) is non-spontaneous because \(I_2\) is not a strong enough oxidizing agent to oxidize water to oxygen. In fact, the reverse reaction (oxidation of \(I^-\) by \(O_2\)) is more favorable in acidic conditions. \[ \boxed{2I_2 + 2H_2O \rightarrow 4HI + O_2} \]
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