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(a) ‘Stability of a crystal is reflected...

(a) ‘Stability of a crystal is reflected in the magnitude of its melting point’. Comment.
(b) The melting points of some compounds are given below : Water = 273 K, Ethyl alcohol = 155.7 K, Diethyl ether = 156.8 K, Methane = 90.5 K. What can you say about the intermolecular forces between these molecules ?

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(a) Higher the melting point, greater are the forces holding the constituent particles together and hence greater is the stability.
(b) The intermolecular forces in water and ethyl alcohol are mainly the hydrogen bonding. Higher melting point of water than alcohol shows that hydrogen bonding in ethyl alcohol molecules is not as strong as in water molecules. Diethyl ether is a polar molecule. The intermolecular forces present in them are dipole-dipole attraction. (London dispersion forces).
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