Answer to Question #280837 in Inorganic Chemistry for danes

Question

Matter exist in different physical forms. The followings questions analyses general characteristics of

matter.

(a) The following table lists the boiling points of compounds of hydrogen. By referring to the type of

intermolecular forces, explain the differences in boiling points between

i. A and B

ii. B and C

iii. C and D

compound formula boiling point/ °C

A methane CH4 -164

B ammonia NH3 -33

C water H2O 100

D silane SiH4 -112

Answer 1

i. The intermolecular force between methane is London dispersion force while that of ammonia is hydrogen bonding. Hydrogen bonds are generally stronger than London dispersion forces hence the reason why ammonia has a high boiling point than methane.

ii. Water has a higher boiling point than ammonia because of the lone pairs. Water has two, ammonia has one. Another reason is the polarity between the O-H bond and N-H bonds. Nitrogen is less electronegative than O hence the lower boiling point.

iii. Intermolecular force of silane is Van der Waals while that of water is hydrogen bonding. Hydrogen bonds are stronger than Van der Waals hence higher boiling points of water compared to silane.