Question 18M.3.sl.TZ2.11
| Date | May 2018 | Marks available | [Maximum mark: 5] | Reference code | 18M.3.sl.TZ2.11 |
| Level | sl | Paper | 3 | Time zone | TZ2 |
| Command term | Discuss, Explain | Question number | 11 | Adapted from | N/A |
Carbon dioxide is a product of the combustion of petrol.
Explain the molecular mechanism by which carbon dioxide acts as a greenhouse gas.
[3]
Any three of:
IR/long wavelength/low frequency radiation radiated/emitted by the Earth’s «surface absorbed in the bonds»
bond length/C=O changes
OR
«asymmetric» stretching of bonds
OR
bond angle/OCO changes
polarity/dipole «moment» changes
OR
dipole «moment» created «when molecule absorbs IR»
«some of» energy is then re-radiated towards «the surface of the» Earth
Do not accept terms such as “reflect” OR “bounced” OR “trapped”.
[3 marks]
Discuss the significance of two greenhouse gases, other than carbon dioxide, in causing global warming or climate change.
[2]
Any two of:
H2O AND «relatively» greater abundance/stable concentration/less effective at absorbing radiation/lower GWP so not much overall effect on global warming/climate change
CH4/N2O/CFCs/SF6/O3/HCFCs AND more effective «than CO2» at absorbing radiation/higher GWP so could contribute to global warming/climate change
PFCs/SF6/NF3/Some CFCs AND have very long life in atmosphere so could contribute «in the future» to global warming/climate change
Accept names or formulas.
Accept two different gases with the same effect for [2].
Award [1 max] for identifying the names/formulas of two greenhouse gases.
Accept “greenhouse factor” for “GWP” but not just “greenhouse effect”.
For M3, do not allow “CFC” alone as only some have long lifetimes (eg, CFC-115, CFC-113).
[2 marks]
