In a series ethane `(CH_(3)-CH_(3))` ethylene `(CH_(2)=CH_(2))` and acetylene `(CH-=CH)` , the C-H bond energy is

Options

A. The same in all the three compounds
B. Greatest in acetylene
C. Greatest in ethylene
D. Greatest in ethane

Answer

To determine the C-H bond energy in the series of ethane (C2H6), ethylene (C2H4), and acetylene (C2H2), we need to analyze the hybridization and bond characteristics of each compound.

### Step-by-Step Solution:

1. **Identify the Structures**:
- **Ethane (C2H6)**: Contains a single bond between two carbon atoms (C-C) and has six hydrogen atoms (H). The structure is:
```
H H
\ /
C - C
/ \
H H
```
- **Ethylene (C2H4)**: Contains a double bond between two carbon atoms (C=C) and has four hydrogen atoms. The structure is:
```
H H
\ /
C = C
/ \
H H
```
- **Acetylene (C2H2)**: Contains a triple bond between two carbon atoms (C≡C) and has two hydrogen atoms. The structure is:
```
H - C ≡ C - H
```

2. **Determine Hybridization**:
- **Ethane**: The hybridization of carbon in ethane is **sp³**. Each carbon forms four sigma bonds (C-H and C-C).
- **Ethylene**: The hybridization of carbon in ethylene is **sp²**. Each carbon forms three sigma bonds and one pi bond (C=C).
- **Acetylene**: The hybridization of carbon in acetylene is **sp**. Each carbon forms two sigma bonds and two pi bonds (C≡C).

3. **Calculate S and P Character**:
- **Ethane (sp³)**: S character = 25%, P character = 75%
- **Ethylene (sp²)**: S character = 33.3%, P character = 66.6%
- **Acetylene (sp)**: S character = 50%, P character = 50%

4. **Analyze Electronegativity and Bond Strength**:
- As the s character increases, the electronegativity of the carbon atom increases, leading to stronger C-H bonds.
- **Ethane**: With sp³ hybridization and low s character, the C-H bond energy is the lowest.
- **Ethylene**: With sp² hybridization and moderate s character, the C-H bond energy is higher than ethane but lower than acetylene.
- **Acetylene**: With sp hybridization and the highest s character, the C-H bond energy is the highest.

5. **Conclusion**:
- The order of C-H bond energy from lowest to highest is: Ethane < Ethylene < Acetylene.
- Therefore, the C-H bond energy is greatest in acetylene.

### Final Answer:
The C-H bond energy is greatest in acetylene (C2H2).

---