Chemistry · Class 11 Science

Ch 6Gaseous State — Class 11 Chemistry, concept-first.

Of the three states of matter, the gaseous state is the simplest to describe mathematically -- and, in the form of the air you breathe every few seconds, the one you depend on most continuously.

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Compressibility Factor

The compressibility factor, , is a dimensionless number measuring how far a real gas's behaviour departs from ideal-gas behaviour under given conditions.

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Chapter contents

The NCERT structure, section by section. Open a section to see its questions, then read the concept-first solution.

Introduction

Of the three states of matter, the gaseous state is the simplest to describe mathematically -- and, in the form of the air you breathe every few seconds, the one you depend on most continuously.

6.1

We can go without food for weeks and without water for days, but without air we last only minutes -- a reminder that the gaseous state, though the simplest of the three states of matter, is also the o…

6.2

The Gas Laws

Gas laws describe how the physical properties of a gas -- pressure, volume, temperature and amount -- relate to one another, and they were arrived at almost entirely by careful experimental study of t…

6.2.1

Boyle's Law: Pressure-Volume Relationship

Robert Boyle investigated, experimentally, how the volume of a fixed amount of gas responds to a change in pressure at constant temperature.

6.2.2

Charles Law (Volume-temperature relationship)

J. A. C. Charles studied how the volume of a fixed mass of gas responds to a change in temperature at constant pressure, and found that volume is directly proportional to the Kelvin temperature (at co…

6.2.3

Gay-Lussac's Law (Pressure-temperature relationship)

Joseph Gay-Lussac established the third pairwise gas law: at constant volume, the pressure of a fixed mass of gas is directly proportional to its Kelvin temperature.

6.2.4

Avogadro's Hypothesis

Amedeo Avogadro proposed that equal volumes of any gas, measured under the same temperature and pressure, contain equal numbers of molecules -- regardless of the gas's chemical identity.

6.3

Ideal gas equation

The complete physical state of a gas needs four variables: pressure P, volume V, temperature T and amount n.

6.4

Mixture of gases - Dalton's law of partial pressures

When several non-reacting gases are mixed together, each component behaves independently of the others -- so it is natural to ask how the pressure of each individual gas contributes to the total press…

6.4.1

Graham's Law of Diffusion

Gas molecules constantly move to occupy all the space available to them. Diffusion is the mixing of one gas's molecules through another gas -- driven by molecules migrating from a region of higher con…

6.5

Deviation from ideal gas behaviour

The ideal gas equation PV = nRT rests on the kinetic theory of gases (its postulates belong properly to the physics syllabus, but the two that matter here are): that individual gas molecules occupy ne…

6.5.1

Compressibility factor Z

The extent to which a real gas departs from ideal behaviour is measured by the compressibility factor, Z, defined as the ratio of the real PV product to the ideal-gas value nRT:

6.5.2

Compressibility factor for real gases

The compressibility factor can be rewritten in a form that makes its physical meaning even more direct.

6.5.3

Van der Waals Equation

J. D. van der Waals carried out the first serious mathematical treatment of real-gas behaviour, by identifying exactly which two ideal-gas assumptions fail and building a correction term for each into…

6.6

Pressure-Volume isotherms of Carbon dioxide

Thomas Andrews produced the first complete experimental picture of how a real substance's pressure, volume and temperature relate to each other across both its gaseous and liquid states, by plotting a…

6.6.1

Derivation of critical constants from van der Waals constant

The critical constants , and are not independent, freely-chosen numbers -- they can be derived directly from the van der Waals constants a and b of a gas, since the critical point is a special feature…

6.7

Liquefaction of gases

Storing gases as liquids matters enormously in practice -- LPG cylinders and rocket propellants are two everyday examples where a gas must be handled in its far more compact liquid form.

Summary

- The state of a gas is fully described by four variables -- pressure (P), volume (V), temperature (T) and number of moles (n) -- and their pairwise relationships are the individual gas laws: Boyle's…

Concept Map

The textbook's concept map is built around the single title "Gaseous State," branching into two broad halves plus two smaller side-branches.

Evaluation

53 Q

This is the textbook's own end-of-chapter evaluation set for the unit, testing the material from the basic pressure-volume-temperature gas laws through to real-gas deviation, the van der Waals equatio…

+Choose the Best Answer25 questions

+Write Brief Answer28 questions

Sample & Board Papers

Sample papers and previous-year board questions for this subject.

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