Ethyl alcohol reacts at a faster rate with `HI` than with `HCl` in forming the corresponding ethyl halides under identical conditions mainly because-

Options

A. `HI`, being a stronger acid, protonates ethyl alcohol at oxygen much better and helps substitution
B. the bond length in `HI` is much shorter than that in `HCl`
C. `I^(-)` is a much better leaving group
D. `I^(-)` is a much better nucleophile than `Cl^(-)`

Answer

To understand why ethyl alcohol reacts faster with HI than with HCl in forming ethyl halides, we can break down the reasoning into several steps:

### Step-by-Step Solution:

1. **Identify the Reactants and Products**:
- Ethyl alcohol (C2H5OH) reacts with hydrogen iodide (HI) and hydrogen chloride (HCl) to form ethyl iodide (C2H5I) and ethyl chloride (C2H5Cl), respectively.

2. **Consider the Nature of the Halides**:
- HI dissociates into H⁺ and I⁻ ions, while HCl dissociates into H⁺ and Cl⁻ ions. The key difference lies in the halide ions: iodide (I⁻) and chloride (Cl⁻).

3. **Analyze the Size of the Halide Ions**:
- Iodide ions (I⁻) are larger in size compared to chloride ions (Cl⁻). This larger size allows the negative charge on I⁻ to be more dispersed.

4. **Evaluate Nucleophilicity**:
- Nucleophilicity refers to the ability of a species to donate an electron pair to an electrophile. Iodide ions (I⁻) are better nucleophiles than chloride ions (Cl⁻) due to their larger size and the ability to stabilize the negative charge more effectively.

5. **Consider the Leaving Group Ability**:
- In nucleophilic substitution reactions, the leaving group is the species that departs with the electrons. Iodide (I⁻) is a better leaving group compared to chloride (Cl⁻) because it can stabilize the negative charge more effectively due to its larger size.

6. **Conclusion**:
- Therefore, ethyl alcohol reacts faster with HI than with HCl because I⁻ is a better nucleophile than Cl⁻, leading to a faster reaction rate in forming ethyl iodide compared to ethyl chloride.

### Final Answer:
Ethyl alcohol reacts at a faster rate with HI than with HCl mainly because I⁻ is a better nucleophile than Cl⁻.