Influence of Intermolecular Forces

Question 1

Hydrogen bonding in water, causes it to have anomalous properties such as

Answer 1

such as high melting and boiling points, high surface tension and a higher density in the liquid than the solid

Question 2

Water has high melting and boiling points due to the the

Answer 2

The strong intermolecular forces of hydrogen bonding between the molecules in both ice (solid H2O) and water (liquid H2O)

A lot of energy is therefore required to separate the water molecules and melt or boil them

Question 3

what is enthalpy of vaporisation

Answer 3

(energy required to boil a substance) of different hydrides

Question 4

The enthalpy changes increase going from H2S to H2Te due to the increased number of……………

This causes an increase in the …………………………………….. as the molecules become larger

Based on this, H2O should have a much lower enthalpy change (around 17 kJ mol-1)
However, the enthalpy change of vaporisation is almost 3 times larger which is caused by the…………. present in water but not in the other hydrides

Answer 4

electrons in the Group 16 elements

instantaneous dipole - induced dipole forces (dispersion forces)

hydrogen bonds

Question 5

Water has a high surface tension
Surface tension is the ability of

Answer 5

a liquid surface to resist any external forces (i.e. to stay unaffected by forces acting on the surface)

Question 6

How does water’s hydrogen bonds allow water to have high surface tension

Answer 6

As a result of hydrogen bonds which exert a strong downwards force on water molecules at the surface,

water has a higher surface tension than most other liquids.

Question 7

Solids are denser than their liquids as

Answer 7

the particles in solids are more closely packed together than in their liquid state

Question 8

The water molecules are packed into an ………… lattice

Answer 8

open

Question 9

How does a open lattice and hydrogen bonds allow , ice to have a lower density than liquid water by about 9%

Answer 9

This way of packing the molecules and the relatively long bond lengths of the hydrogen bonds means that the water molecules are slightly further apart than in the liquid form

When water freezes into ice, water molecules become arranged into a 3D network where each water molecule is connected to four other water molecules by hydrogen bonds. As a result of this regular lattice structure, the water molecules in solid ice are further apart than the molecules in liquid water. The structure is more open in ice which makes it less dense than water.

Question 10

Ice floats on water because of

Answer 10

ice’s lower density.