(i) Distinguish between the thermal properties of water and methane.

(ii) Explain the reasons for the unique thermal properties of water.

Using the diagram, explain the interaction of short and long wave radiation with greenhouse gases in the atmosphere.

(i)

Boiling point of water is greater than methane

Melting point of water is greater than methane

Latent heat of vaporization of water is greater than methane
OR
specific heat capacity of water is greater than methane

(ii)

Water is polar
OR
O atom more negative
OR
H atoms more positive

This causes «strong» hydrogen bonds to form between the molecules

Which require more/high amount of energy to break

Which increases the melting/boiling/latent heat properties

Short wave radiation/UV «shown as» having its origin in the Sun gives off light as short radiation

Short wave radiation/UV «shown as» passing through the greenhouse gases «some reflected»

Some short wave radiation/UV is absorbed by the Earth and some is reflected

The reflected radiation is long wave radiation «reflected as heat»

Long wave radiation/IR «shown as» being unable to pass through/being absorbed/reflected by the greenhouse gases

Award marks for diagrammatic explanations of these marking points.
Accept UV and IR as long as they are drawn with the correct wavelength.

(i) The expression ‘thermal properties’ seemed to confuse weaker candidates, who looked ahead to part b and tried to compare them as greenhouse gases. Perhaps the use of ‘physical properties’ might have been better. Many were able to state, for example, that water has a high boiling point, but did not get the mark as they did not continue to say that it was much higher than methane. 

(ii) Most remembered about hydrogen bonds, but lost the mark for forgetting to state that they are between molecules. 

The writer of this question presumed that the more visual learners would use the diagram to produce an annotated response. In fact, very few used the diagram at all. The difference between long and short wavelengths was very confused, and weaker candidates were obsessed with explaining the composition of the greenhouse gases, and the role of the ozone layer (usually incorrectly). As a major problem affecting the planet, there seemed to be a lot of confusion.