Select the correct relation of interaction energy of dipole-dipole force in stationary polar molecule with internuclear distance ®

Options

A. Interaction energy `prop 1/r`
B. Interaction energy `prop 1/r^2`
C. Interaction energy `prop 1/r^3`
D. Interaction energy `prop 1/r^5`

Answer

To solve the problem of determining the correct relation of interaction energy of dipole-dipole forces in stationary polar molecules with respect to the internuclear distance (r), we can follow these steps:

### Step 1: Understand Dipole-Dipole Interaction
Dipole-dipole interactions occur between polar molecules that have permanent dipoles. The interaction energy depends on the orientation of the dipoles and the distance between them.

### Step 2: Recall the Formula for Dipole-Dipole Interaction
The interaction energy (U) between two dipoles (μ) can be expressed as:
\[ U \propto \frac{1}{r^3} \]
This means that the interaction energy is inversely proportional to the cube of the distance between the dipoles.

### Step 3: Write the Relation
From the above understanding, we can conclude that:
\[ U \propto \frac{1}{r^3} \]
This indicates that as the distance (r) increases, the interaction energy decreases rapidly.

### Step 4: Conclusion
The correct relation of interaction energy of dipole-dipole forces in stationary polar molecules with internuclear distance (r) is:
\[ U \propto \frac{1}{r^3} \]