8.3. Homogeneous and heterogeneous catalysts
A subsection of Chemistry, 9701, through 8. Reaction kinetics
Listing 10 of 23 questions
Trihalomethanes are organic molecules in which three of the hydrogen atoms of methane are replaced by halogen atoms, for example CHCl 3. CHCl 3 is a colourless liquid with a high vapour pressure. Explain what is meant by high vapour pressure. An important reaction of CHCl 3is the manufacture of CHCl F2, using the following reversible reaction. CHCl 3+ 2HFCHCl F2+ 2HCl Use the data to calculate the enthalpy change of reaction, ΔHr , for the formation of CHCl F2as shown in the equation. compound enthalpy change of formation, ΔHf / kJ mol–1 CHCl 3–103.2 CHCl F2– 482.2 HF–273.3 HCl –92.3  enthalpy change of reaction, ΔHr = kJ mol–1 The reaction in is carried out using a heterogeneous catalyst. Explain fully the meaning of the terms heterogeneous and catalyst. heterogeneous catalyst  CHCl F2 was used as an alternative to chlorofluorocarbons (CFCs). CHCl F2 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. Explain how CHCl F2may contribute to this effect. Suggest another environmental problem associated with the use of CHCl F2. CHCl F2 is also used to produce the monomer tetrafluoroethene, C2F4. This monomer can be used to produce poly, PTFE. State the type of polymerisation that occurs during the production of PTFE. Draw the repeat unit of PTFE.  Suggest why PTFE is used as a coating for cooking pans. Waste disposal can cause litter problems. State two other difficulties associated with the disposal of PTFE.  
9701_w18_qp_21
THEORY
2018
Paper 2, Variant 1
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Trihalomethanes are organic molecules in which three of the hydrogen atoms of methane are replaced by halogen atoms, for example CHCl 3. CHCl 3 is a colourless liquid with a high vapour pressure. Explain what is meant by high vapour pressure. An important reaction of CHCl 3is the manufacture of CHCl F2, using the following reversible reaction. CHCl 3+ 2HFCHCl F2+ 2HCl Use the data to calculate the enthalpy change of reaction, ΔHr , for the formation of CHCl F2as shown in the equation. compound enthalpy change of formation, ΔHf / kJ mol–1 CHCl 3–103.2 CHCl F2– 482.2 HF–273.3 HCl –92.3  enthalpy change of reaction, ΔHr = kJ mol–1 The reaction in is carried out using a heterogeneous catalyst. Explain fully the meaning of the terms heterogeneous and catalyst. heterogeneous catalyst  CHCl F2 was used as an alternative to chlorofluorocarbons (CFCs). CHCl F2 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. Explain how CHCl F2may contribute to this effect. Suggest another environmental problem associated with the use of CHCl F2. CHCl F2 is also used to produce the monomer tetrafluoroethene, C2F4. This monomer can be used to produce poly, PTFE. State the type of polymerisation that occurs during the production of PTFE. Draw the repeat unit of PTFE.  Suggest why PTFE is used as a coating for cooking pans. Waste disposal can cause litter problems. State two other difficulties associated with the disposal of PTFE.  
9701_w18_qp_23
THEORY
2018
Paper 2, Variant 3
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Questions Discovered
23