Reaction for `6Kl+2FeCl_3 to 2Fel+6KCl+2I_2` has been found to be third order kinetically because it is supposed to occur in steps. What can be its molecularity?

Options

A. 3
B. 8
C. -1
D. 2

Answer

To determine the molecularity of the reaction given by the equation:

\[ 6 \text{KI} + 2 \text{FeCl}_3 \rightarrow 2 \text{FeI} + 6 \text{KCl} + 2 \text{I}_2 \]

we can follow these steps:

### Step 1: Understand the Concepts of Order and Molecularity
- **Order of a Reaction**: This is the sum of the powers of the concentration terms in the rate law expression. It reflects how the rate of reaction depends on the concentration of the reactants.
- **Molecularity of a Reaction**: This is the number of reactant molecules involved in an elementary step of a reaction. It can be classified as unimolecular (1), bimolecular (2), or termolecular (3) based on the number of molecules.

### Step 2: Analyze the Given Reaction
The reaction is given as:
\[ 6 \text{KI} + 2 \text{FeCl}_3 \rightarrow 2 \text{FeI} + 6 \text{KCl} + 2 \text{I}_2 \]

### Step 3: Count the Reactant Molecules
- From the reactants, we have:
- 6 molecules of KI
- 2 molecules of FeCl3

Adding these together gives:
\[ 6 + 2 = 8 \text{ molecules} \]

### Step 4: Determine the Molecularity
Since molecularity refers to the total number of reactant molecules that are involved in the rate-determining step of the reaction, we conclude that:
- The molecularity of the reaction is 8.

### Conclusion
Thus, the molecularity of the reaction \( 6 \text{KI} + 2 \text{FeCl}_3 \rightarrow 2 \text{FeI} + 6 \text{KCl} + 2 \text{I}_2 \) is 8.

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