Federal Board Chemistry XI Chapter# 05 (Exercise Notes)

  1. Give the general properties of liquids as to
  2. a) Diffusion

Liquid molecules have kinetic energy. They can move from place to place. The diffusion n liquids is due to movement of molecules from one place to another. Due to limited movement of molecule, the rate of diffusion decreases.

E.g. when a drop of ink is added to water it diffuses slowly, it is because there are small empty spaces between the molecules. The diffusion between closely packed molecules of liquids is slow due to less collision between them.

  1. b) Compression

In liquids molecules are in close contact, therefore, it cannot be compressed significantly by applying pressure. E.g. when pressure on water is increase from one to two atmospheres, its volume is reduced to 0.0045 percent which is negligible. Howeverthe same pressure reduces the volume of a gas up to 50 percent.

  1. What are intermolecular forces?

The forces of attractions among the molecules of a substance are called intermolecular forces. E.g. water exists as a liquid due to inter molecular forces called Hydrogen bonds. – The forces of attraction among molecules of non-polar substances are called Van der Waal’s forces. – The physical properties of liquids depend upon the strength of these forces.

Examples: Dipole-Dipole forces, London Dispersion forces, Hydrogen bonding etc.

  1. What are the types of intermolecular forces, give examples?

The intermolecular forces are of five types

  • Dipole-dipole forces: e.g. between HCl molecule (polar)
  • – Ion-dipole forces: e.g. between H+ ions and water molecules
  • – Dipole-induced dipole forces: e.g. between He gas (non-polar) and HCl gas (polar)
  • – London Dispersion forces: e.g. forces between He molecules (non-polar)
  • – Hydrogen bonding: e.g. forces between water molecules

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