Trihalomethanes are organic molecules in which three of the hydrogen atoms of methane are replaced by halogen atoms, for example CHCl3.

1. (a)(i)CHCl3 is a colourless liquid with a high vapour pressure. Explain what is meant by high vapour pressure.[2]
2. (a)(ii)An important reaction of CHCl3(g) is the manufacture of CHClF2(g), using the following reversible reaction. CHCl3(g) + 2HF(g) ⇌ CHClF2(g) + 2HCl(g) Use the data to calculate the enthalpy change of reaction, ΔHr, for the formation of CHClF2(g) as shown in the equation. compound | enthalpy change of formation, ΔHf/kJ mol⁻¹ ---|--- CHCl3(g) | -103.2 CHClF2(g) | -482.2 HF(g) | -273.3 HCl(g) | -92.3 enthalpy change of reaction, ΔHr = .......................... kJ mol⁻¹[3]
3. (a)(iii)The reaction in (ii) is carried out using a heterogeneous catalyst. Explain fully the meaning of the terms heterogeneous and catalyst.[3]
4. (b)(i)CHClF2 was used as an alternative to chlorofluorocarbons (CFCs). CHClF2 should no longer be used because it was found to contribute to the enhanced greenhouse effect. Give the meaning of the term enhanced greenhouse effect.[1]
5. (b)(ii)Explain how CHClF2(g) may contribute to this effect.[2]
6. (b)(iii)Suggest another environmental problem associated with the use of CHClF2.[1]
7. (c)(i)CHClF2 is also used to produce the monomer tetrafluoroethene, C2F4. This monomer can be used to produce poly(tetrafluoroethene), PTFE. State the type of polymerisation that occurs during the production of PTFE.[1]
8. (c)(ii)Draw the repeat unit of PTFE.[1]
9. (c)(iii)Suggest why PTFE is used as a coating for cooking pans.[1]
10. (c)(iv)Waste disposal can cause litter problems. State two other difficulties associated with the disposal of PTFE. 1 2[2]