Chemistry Class-11: Chapter –5. States of Matter Part – 4

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Question: 21

Use the information and data given below to answer the questions (a) to (c):

• Stronger intermolecular forces result in higher boiling point.

• Strength of London forces increases with the number of electrons in the molecule.

• Boiling point of and HI are and respectively.

(a) Which type of intermolecular forces are present in the molecules and ?

(b) Looking at the trend of boiling points of and , explain out of dipole-dipole interaction and London interaction, which one is predominant here.

(c) Why is boiling point of hydrogen fluoride highest while that of hydrogen chloride lowest?


(a) In and , dipole-dipole and London forces because molecules possess permanent dipole. In dipole-dipole, London forces and hydrogen bonding.

(b) Electronegativity of chlorine, bromine and iodine decreases in the order:

Therefore, dipole moment should decrease from to . Thus, dipole-dipole interaction should decrease from to . But boiling point increases on moving from to . This means that London forces are predominant. This is so because London forces increase as the number of electrons in a molecule increases and in this case number of electrons is increasing from towards .

(c) Hydrogen fluoride has highest dipole moment due to highest Electronegativity of fluorine and hydrogen bonding is also present in it. Therefore, has highest boiling point.

Question: 22

What will be the molar volume of nitrogen and argon at and ?


Question: 23

A gas that follows Boyle’s law, Charle’s law and Avogadro’s law is called an ideal gas. Under what conditions a real gas would behave ideally?


Low pressure and high temperature

Question: 24

Two different gases ‘A’ and ‘B’ are filled in separate containers of equal capacity under the same conditions of temperature and pressure. On increasing the pressure slightly the gas ‘A’ liquefies but gas B does not liquefy even on applying high pressure until it is cooled. Explain this phenomenon.


Gas ‘A’ is at or below its critical temperature and gas ‘B’ is at a temperature higher than critical temperature.

Question: 25

Value of universal gas constant (R) is same for all gases. What is its physical significance?


Unit of R depends upon those units in which p, and T are measured, . If pressure is measured in Pascal, per mole volume is measured in and temperature is measured in Kelvin then. Units of ‘R’ . Jule is the unit of work done so ‘R’ is work done per mole per Kelvin.

Question: 26

One of the assumptions of kinetic theory of gases states that “there is no force of attraction between the molecules of a gas.” How far is this statement correct? Is it possible to liquefy an ideal gas? Explain.


In the absence of intermolecular forces of attraction, it will not be possible to liquefy ideal gas.

Question: 27

The magnitude of surface tension of liquid depends on the attractive forces between the molecules. Arrange the following in increasing order of surface tension:


Question: 28

Pressure exerted by saturated water vapour is called aqueous tension. What correction term will you apply to the total pressure to obtain pressure of dry gas?


Question: 29

Thermal energy. It is a measure of average kinetic energy of particles. It increases with increase in temperature.


Name the energy which arises due to motion of atoms or molecules in a body. How is this energy affected when the temperature is increased?

Question: 30

Name two intermolecular forces that exist between HF molecules in liquid state.


(i) Dipole - dipole interaction

(ii) Hydrogen - bonding

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