Join WhatsApp Icon JEE WhatsApp Group
Question 37

The correct statement(s) about intermolecular forces is(are)

Intermolecular interaction energies are obtained by applying Coulomb’s law to the various charge distributions that can exist on (or be induced in) molecules - permanent charges, permanent dipoles, induced dipoles, etc. The distance dependence and, in some cases, the temperature dependence of the average energy decide whether a given statement is true or false.

Option A
• Potential energy between two point charges (say $$q_1$$ and $$q_2$$) is $$U_{qq}= \dfrac{q_1q_2}{4\pi\varepsilon_0\,r} \propto \dfrac{1}{r}$$.
• Potential energy between a point charge $$q$$ and a point dipole of moment $$\mu$$ (the dipole oriented so that the interaction is maximum) is $$U_{q\mu}= -\dfrac{q\mu}{4\pi\varepsilon_0\,r^{2}} \propto \dfrac{1}{r^{2}}$$.
Because $$1/r^{2}$$ tends to zero faster than $$1/r$$ when $$r\rightarrow\infty$$, the charge-dipole energy approaches zero more rapidly than the charge-charge energy. Option A claims the opposite, hence it is false.

Option B
For two freely rotating permanent dipoles, the orientation-averaged (thermal average) interaction energy has Keesom form
$$\langle U_{\mu\mu}\rangle = -\dfrac{2\mu_1^{2}\mu_2^{2}}{3(4\pi\varepsilon_0)^{2}k_{\mathrm B}T\,r^{6}} \propto -\dfrac{1}{T\,r^{6}}.$$
Thus the energy falls off as $$1/r^{6}$$, not $$1/r^{3}$$. Therefore Option B is false.

Option C
Dipole-induced dipole interaction (Debye interaction): a permanent dipole $$\mu$$ induces a dipole $$\alpha \,E$$ in a neighbouring polarisable molecule (where $$\alpha$$ is its polarisability and $$E$$ the electric field of the permanent dipole). The orientation-averaged energy is
$$\langle U_{\mu\text{-ind}}\rangle = -\dfrac{\mu^{2}\alpha}{(4\pi\varepsilon_0)^{2}\,2\,r^{6}},$$
which contains no temperature term. Hence it is independent of temperature. Option C is true.

Option D
Even molecules with no permanent dipole can attract each other through London dispersion forces. A momentary (instantaneous) dipole in one molecule induces a dipole in the other, giving an average interaction energy
$$\langle U_{\text{disp}}\rangle = -\dfrac{3h\nu\,\alpha_1\alpha_2}{4(4\pi\varepsilon_0)^{2}\,r^{6}},$$
which is always attractive. Hence non-polar molecules do attract one another despite lacking permanent dipoles. Option D is true.

Therefore the correct statements are:
Option C (dipole-induced dipole energy is temperature-independent) and
Option D (non-polar molecules attract each other via dispersion forces).

Final answer: Option C and Option D.

Get AI Help

Create a FREE account and get:

  • Free JEE Advanced Previous Papers PDF
  • Take JEE Advanced paper tests

JEE Quant Questions | JEE Quantitative Ability

JEE DILR Questions | LRDI Questions For JEE

JEE Verbal Ability Questions | VARC Questions For JEE

Free JEE Topicwise Questions

JEE StatisticsJEE Carboxylic AcidsJEE Work, Energy & PowerJEE EMF & Circuit AnalysisJEE Chemical ThermodynamicsJEE Vector AlgebraJEE Practical Organic ChemistryJEE ProbabilityJEE Sets, Relations & FunctionsJEE Three Dimensional GeometryJEE Chemical KineticsJEE Rotational MotionJEE Alternating CurrentsJEE Nitrogen-Containing CompoundsJEE ElasticityJEE Permutations & CombinationsJEE Basic Principles of Organic ChemistryJEE Coordination CompoundsJEE Heat TransferJEE JEE 2D GeometryJEE Trigonometric FunctionsJEE LimitsJEE BiomoleculesJEE ElectrochemistryJEE Binomial TheoremJEE d and f-Block ElementsJEE Hydrocarbons - AlkenesJEE Indefinite IntegrationJEE Current & ResistanceJEE DeterminantsJEE Kinetic Theory of GasesJEE Purification & CharacterisationJEE WavesJEE Surface TensionJEE Redox ReactionsJEE DifferentiationJEE Units & MeasurementsJEE Periodic Table & PeriodicityJEE Laws of ThermodynamicsJEE Complex NumbersJEE Simple Harmonic MotionJEE Basic Concepts in ChemistryJEE EquilibriumJEE Electromagnetic WavesJEE Electric Charges & FieldsJEE Kinematics - 2D MotionJEE Wave OpticsJEE Laboratory Experiments - XIJEE Sequences & SeriesJEE Electric Potential & CapacitanceJEE CirclesJEE p-Block Elements (Groups 13-18)JEE Electromagnetic InductionJEE Hydrocarbons - AromaticJEE Magnetic Effects of CurrentJEE MatricesJEE Laws of MotionJEE Inverse Trigonometric FunctionsJEE Alcohols, Phenols & EthersJEE Atoms & NucleiJEE Straight LinesJEE Hydrocarbons - AlkynesJEE Kinematics - 1D MotionJEE Fluid MechanicsJEE Ray OpticsJEE Continuity & DifferentiabilityJEE Definite IntegrationJEE Applications of DerivativesJEE Atomic StructureJEE Aldehydes & KetonesJEE Electronic DevicesJEE Differential EquationsJEE Dual Nature of Matter & RadiationJEE Chemical Bonding & Molecular StructureJEE Organic Compounds with HalogensJEE Conic SectionsJEE Hydrocarbons - AlkanesJEE Number SystemJEE Quadratic EquationsJEE SolutionsJEE Magnetism & Magnetic MaterialsJEE Gravitation
Ask AI