Question

Stability of a crystal is reflected in the magnitude of its melting points
Comment. Melting point of solid water, ethyl alcohol, diethyl ether and methan from a data book. What can you say about the intermolecular forces between these molecules ?

Answer 1

Explanation:

Collect melting point of water, ethyl alcohol, diethyl ether, and methane from a data book. What can you say about the intermolecular forces between these molecules.

Answer 2

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Explanation. The melting point of a crystal depends upon the magnitude of forces holding the constituent particles together, which determine the stability. Higher the melting points, greater are the forces holding the constituent particles together and hence greater is the stability.

For example, Ionic crystals such as NaCl KNO3 etc. have very high melting points and are stable. On the other hand, molecular solids such as naphthalene, iodine, etc. are less stable because they have low values of melting point.

The melting point of some compounds are :

Water = 273 K, Ethyl alchol = 155.8 K, Diethyl ether = 156.8 K, and Methane = 90.5 K.

The intermolecular forces in water and ethyl alcohol are mainly hydrogen bonding. The higher melting point of water than ethyl alcohol indicates that the hydrogen bonding in water is stronger than in ethyl alcohol. Diethyl ether is polar molecule and, therefore, the intermolecular forces in diethyl ether are dipole–dipole interactions. On the other hand, methane is a non polar molecule and the only force present in them are the weak van der Walls forces. These are weaker than dipole–dipole interactions and hence methane has very low melting point than diethyl ether.