JEE Advanced · Chemistry

States of Matter

Select the correct particle and intermolecular-force model for gases and liquids before choosing a gas law or a property relationship such as vapour pressure, surface tension or viscosity.

Subject
Chemistry
Syllabus unit
States of Matter: Gases and Liquids (JEE Advanced 2026 only; not a named JEE Main 2026 unit)
Updated
8 September 2026
  • Listed in JEE Advanced 2026
  • Not listed as a named unit in JEE Main 2026 Chemistry
  • No invented weightage, question counts or trend percentages

Content status: draft. Verified academic content for this page has not been loaded yet, so the page is excluded from search indexing and the sitemap.

In short

A States of Matter problem is a model-selection problem. Ask how freely the particles move, how their separation compares with molecular size, whether intermolecular attractions matter, and which macroscopic variable is observed.

Use an ideal-gas model only when its assumptions are acceptable. Use an intermolecular-force model for liquid vapour pressure, surface tension, viscosity, and real-gas behaviour.

Syllabus mapping

  • Unit
    States of Matter: Gases and Liquids (JEE Advanced 2026 only; not a named JEE Main 2026 unit)
    Topics
    Gas laws and the ideal-gas model, Real-gas behaviour and departures from ideality, Kinetic theory of gases and molecular velocities, Partial pressure and diffusion, Intermolecular interactions, Liquid vapour pressure, Surface tension, Viscosity

What this chapter contains and why it matters

  • Question
    What is the chapter about?
    Direct answer
    Choosing the correct particle and intermolecular-force model for gases and liquids, and selecting the matching property relation for vapour pressure, boiling, surface tension, or viscosity.
  • Question
    What is the central method choice?
    Direct answer
    Decide particle freedom and the balance between thermal motion and attraction, confirm whether the ideal-gas model is acceptable, and only then select a gas-law, vapour-pressure, surface-tension, or viscosity relation.
  • Question
    Where do most mistakes begin?
    Direct answer
    Treating vapour pressure as a fixed material constant independent of temperature, saying boiling begins when vapour pressure is zero, and treating surface tension as a bulk pressure.
  • Question
    What should come before States of Matter?
    Direct answer
    Mole Concept for amount of substance, Chemical Bonding for intermolecular forces, and Solutions for related composition and vapour-pressure reasoning.
  • Question
    What comes after it?
    Direct answer
    Gaseous State develops equation-level gas-law and kinetic-theory depth; Thermodynamics connects state properties to energy relations.

The official JEE documents define content scope. They do not publish chapter weightage, so none is asserted here.

Official JEE syllabus mapping for States of Matter

Verified against the current JEE Main 2026 and JEE Advanced 2026 syllabus documents on 8 September 2026. States of Matter is an Advanced-only current-syllabus umbrella, not a separate JEE Main 2026 unit.

  • Concept group
    States of Matter as a named unit
    JEE Main 2026
    No named States of Matter unit appears in the official Main syllabus. Related ideas occur within other units, but they do not establish this chapter as current Main scope.
    JEE Advanced 2026
    Explicitly listed as States of Matter: Gases and Liquids, covering gas laws, ideal and real-gas ideas, kinetic theory, velocities, partial pressure, diffusion, intermolecular interactions, and liquid vapour pressure, surface tension, and viscosity.
    Preparation note
    Treat this as an Advanced-only current-cycle chapter, not a Main 2026 topic.
  • Concept group
    Overlaps with other Main units
    JEE Main 2026
    If an official Main item tests an overlapping concept from another current unit, that item belongs to that unit, not to States of Matter.
    JEE Advanced 2026
    Not applicable; the section is self-contained in the Advanced syllabus.
    Preparation note
    Tag any overlapping Main content to its own unit rather than calling it States of Matter scope.

Sources: JEE Main 2026 syllabus and JEE Advanced 2026 syllabus, both linked in the sources section below.

Before this chapter

Prerequisites: what you should know before States of Matter

  • Prerequisite
    Amount of substance
    You are ready if you can…
    Convert between mass, moles and particle count.
    If not, repair this first
    Revise Mole Concept before working with any gas or liquid property.
  • Prerequisite
    Temperature in kelvin
    You are ready if you can…
    Use absolute temperature consistently in gas and vapour-pressure relations.
    If not, repair this first
    Practise Celsius-to-Kelvin conversion before substituting into any relation.
  • Prerequisite
    Pressure and volume units
    You are ready if you can…
    Convert between common pressure and volume unit systems.
    If not, repair this first
    Review unit conversion for pressure (Pa, atm) and volume (L, m^3).
  • Prerequisite
    Molecular polarity and intermolecular forces
    You are ready if you can…
    Predict whether a substance has significant dipole-dipole, hydrogen-bonding, or dispersion interactions.
    If not, repair this first
    Revisit Chemical Bonding before deciding whether ideal-gas or real-gas behaviour applies.

This is a readiness check, not a weightage or scoring-priority list.

Concepts in this chapter

1. Compare particle freedom before selecting a model

Gas particles explore the container; liquid particles remain close but can rearrange.

Gas particles explore the container; liquid particles remain close but can rearrange. This difference in freedom of motion is the first decision point for choosing a model.

2. Weigh thermal motion against attractive interactions

Thermal motion tends to disperse particles. Attractive interactions tend to keep them close. Which effect dominates determines whether a gas, liquid, or intermediate behaviour is observed.

3. Know what the ideal-gas model neglects

The ideal-gas model neglects particle volume and intermolecular forces.

The ideal-gas model neglects particle volume and intermolecular forces. It is a simplification, valid only under conditions where those neglected effects stay small.

4. Recognise when real-gas behaviour appears

Real behaviour appears when the neglected particle volume and intermolecular attractions are no longer small, typically at high pressure or low temperature.

5. Treat the liquid surface as a distinct environment

Molecules at a surface have a different balance of attractions from molecules in the bulk.

Molecules at a surface have a different balance of attractions from molecules in the bulk. This imbalance is the physical basis of surface tension.

6. Treat viscosity as condition-dependent

Viscosity describes resistance to flow and is condition-dependent, changing with temperature and with the identity of the fluid.

7. Hand off to Gaseous State for equation-level gas depth

Once a problem is identified as gas-law or kinetic-theory depth, this chapter hands off to Gaseous State, which owns the equation-level treatment of that model.

Method selector: choose the model before the relation

Match the question signal to the first model and its required condition check.

  • Question signal
    Pressure, volume, amount, temperature
    Start with
    Gas equation
    Required condition check
    Kelvin scale, units, ideality
  • Question signal
    Gas mixture
    Start with
    Partial-pressure model
    Required condition check
    Non-reacting ideal-mixture assumption
  • Question signal
    High pressure or low temperature
    Start with
    Real-gas model
    Required condition check
    Molecular volume and attraction
  • Question signal
    Evaporation or boiling
    Start with
    Vapour-pressure model
    Required condition check
    Temperature and external pressure
  • Question signal
    Surface formation or droplets
    Start with
    Surface-tension model
    Required condition check
    Interface, temperature, contamination
  • Question signal
    Resistance to liquid flow
    Start with
    Viscosity model
    Required condition check
    Temperature and fluid identity

Condition-aware property records

  • Record
    Vapour pressure
    Meaning
    Equilibrium pressure of vapour above its liquid in a closed system at a stated temperature
    Units
    Pa in SI
    Conditions and limitation
    Pure substance and temperature must be identified; not a fixed material constant independent of temperature
  • Record
    Normal boiling point
    Meaning
    Temperature at which vapour pressure equals standard atmospheric pressure
    Units
    K in SI reporting
    Conditions and limitation
    Defined using the specified standard pressure; boiling does not begin when vapour pressure reaches zero
  • Record
    Surface tension (gamma)
    Meaning
    Force per unit length, equivalently surface energy per unit area under the appropriate definition
    Units
    N m^-1, equivalent to J m^-2
    Conditions and limitation
    Interface and temperature matter; it is not a bulk pressure
  • Record
    Dynamic viscosity (eta)
    Meaning
    Proportionality describing internal resistance to shear flow for a Newtonian fluid
    Units
    Pa s
    Conditions and limitation
    Temperature and fluid model matter; not every fluid behaves as an ideal Newtonian fluid

Worked examples

Explain why stronger intermolecular attraction usually lowers vapour pressure at the same temperature.

Answer: At the same temperature, fewer molecules have enough energy to escape and remain in the vapour phase at equilibrium, so vapour pressure is lower for stronger intermolecular attraction.

Vapour pressure at equilibrium reflects the balance between molecules escaping into the vapour phase and molecules returning to the liquid.

Stronger intermolecular attraction raises the energy barrier for a molecule to escape the liquid surface.

At the same temperature, fewer molecules have enough energy to escape and remain in the vapour phase at equilibrium, so the equilibrium vapour pressure is lower.

Common mistakes and what they actually indicate

  • Treating States of Matter as a current JEE Main 2026 Chemistry unit.

    Needs review

    Why it happens

    No named States of Matter unit appears in the official Main syllabus, even though related ideas occur within other units.

    How it is corrected

    Check the official syllabus mapping table on this page before assuming Main-exam relevance.

  • Treating vapour pressure as a fixed material constant independent of temperature.

    Knowledge gap

    Why it happens

    Vapour pressure is an equilibrium property defined at a stated temperature and changes with it.

    How it is corrected

    Always state the temperature alongside any vapour-pressure value used or compared.

  • Saying boiling begins when vapour pressure is zero.

    Recall gap

    Why it happens

    The normal boiling point is defined as the temperature where vapour pressure equals standard atmospheric pressure, not zero.

    How it is corrected

    Compare vapour pressure to the external (often standard atmospheric) pressure to define boiling.

  • Treating surface tension as a bulk pressure.

    Knowledge gap

    Why it happens

    Surface tension is a force per unit length (or energy per unit area) at an interface, not a pressure acting throughout the bulk.

    How it is corrected

    Keep surface tension's units (N/m or J/m^2) distinct from bulk pressure units (Pa).

  • Assuming all fluids behave as ideal Newtonian fluids when applying a viscosity relation.

    Decision / selection error

    Why it happens

    Dynamic viscosity as a single proportionality constant is defined for a Newtonian fluid; not every real fluid satisfies that model.

    How it is corrected

    Confirm the fluid and temperature model before applying a simple viscosity relation.

  • Making a real-gas comparison or current-scope statement without primary support.

    Needs review

    Why it happens

    Comparative claims and current-scope statements must trace to the official syllabus or verified academic material.

    How it is corrected

    Check the property record and its source note before repeating a comparison or scope claim.

FAQ

States of Matter — questions

Straight answers about how Rank Sarthi fits into serious exam preparation.

No named States of Matter unit appears in the official Main syllabus.

Sources and provenance

Evidence boundary: this page states plainly that no named States of Matter unit appears in the current JEE Main 2026 Chemistry syllabus, and that the current JEE Advanced 2026 syllabus explicitly includes gases, liquids and intermolecular-interaction scope. Any official Main item testing an overlapping concept is tagged to its own current unit, not treated as States of Matter scope. No chapter weightage, question frequency or forecast is asserted.

Last updated
8 September 2026

Contributor requirements for this page

  • Author: a JEE Physical Chemistry educator who teaches particle models and intermolecular forces.
  • Academic reviewer: postgraduate qualification in Physical Chemistry, Chemical Physics, or a closely related discipline, with documented subject expertise in molecular thermodynamics and fluid properties.
  • Independent checker: a chemistry educator or subject editor who verifies every model assumption, definition, unit and comparative claim separately from the author.
  • No contributor is named on this page until their identity and qualification are verified, so no author, reviewer or rating is displayed yet.