JEE Main · 2019 · Shift-IIeasyPB12-027

Among the following reactions of hydrogen with halogens, the one that requires a catalyst is:

p-Block Elements (Class 12) · Class 12 · JEE Main Previous Year Question

Question

Among the following reactions of hydrogen with halogens, the one that requires a catalyst is:

Options
  1. a

    H2+Cl2→2HCl\mathrm{H_2 + Cl_2 \rightarrow 2HCl}

  2. b

    H2+I2→2HI\mathrm{H_2 + I_2 \rightarrow 2HI}

    ✓
  3. c

    H2+F2→2HF\mathrm{H_2 + F_2 \rightarrow 2HF}

  4. d

    H2+Br2→2HBr\mathrm{H_2 + Br_2 \rightarrow 2HBr}

Correct Answerb

H2+I2→2HI\mathrm{H_2 + I_2 \rightarrow 2HI}

Detailed Solution

Strategy: Consider the reactivity and activation energy down the Halogen group.

Step 1: Reactivity Trends Reactivity with \ceH2\ce{H2} decreases as \ceF2>Cl2>Br2>I2\ce{F2 > Cl2 > Br2 > I2}:

  • \ceF2\ce{F2}: Violent/spontaneous even in the dark.
  • \ceCl2\ce{Cl2}: Requires sunlight (photochemical).
  • \ceBr2\ce{Br2}: Requires heating.
  • \ceI2\ce{I2}: Requires heating and a catalyst (\cePt\ce{Pt}) due to its low reactivity and the reversible nature of the reaction.

Step 2: Selection The reaction with Iodine (\ceI2)(\ce{I2}) is the one typically requiring a catalyst.

Answer: (Option) [b] \ceH2+I2−>2HI\boxed{\text{Answer: (Option) [b] $\ce{H2 + I2 -> 2HI}$}}

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