Orientation polarization in gases and temperature dependence State whether the following statement is true or false: “For a polyatomic gas composed of polar molecules, the orientation (dipolar) polarization is inversely proportional to absolute temperature.”

Introduction / Context:
Dielectric polarization in gases includes contributions from electronic distortion and, for polar molecules, orientation of permanent dipoles. The temperature dependence of the orientation component is a classic result used in dielectric spectroscopy and in the Debye model.

Given Data / Assumptions:

• Gas of polyatomic, polar molecules with permanent dipole moment.
• Low to moderate fields; linear response applies.
• No significant clustering or association effects.

Concept / Approach:
In the Debye model, the orientation polarization P_or arises from partial alignment of permanent dipoles against thermal agitation. The average alignment increases with field but decreases with temperature because randomizing thermal motion is stronger at higher T. Quantitatively, the orientational contribution to permittivity obeys P_or ∝ (N * μ^2 / (k * T)) * E, leading to ε_r − 1 containing a term ∝ 1/T for polar gases.

Step-by-Step Solution:
Identify mechanism: permanent dipoles reorient in an applied E.Thermal energy kT resists alignment; higher T → less average alignment.Therefore, orientation polarization scales inversely with T → statement is true.

Verification / Alternative check:
Measurements of ε_r versus temperature for gases like HCl or H_2O vapor show ε_r decreasing with increasing T at fixed pressure, consistent with P_or ∝ 1/T.

Why Other Options Are Wrong:
“False” and “directly proportional to temperature” contradict Debye polarization theory. “Independent of temperature” applies only to nonpolar gases for the electronic component; it is not correct for polar orientation polarization. “True only at cryogenic temperatures” is too restrictive; the 1/T behavior holds over a broad temperature range before other effects dominate.

Common Pitfalls:

• Failing to distinguish polar from nonpolar gases (nonpolar gases lack orientation polarization).
• Mixing electronic (weakly T-dependent) and orientational (strongly T-dependent) contributions.

Final Answer:
True