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chemistry
intermolecular forces
| Question | Answer |
|---|---|
| Explain the trend in boiling temperature of these halogenoalkanes by comparing the intermolecular forces involved. Detailed explanations of the forces involved are not required. (4) | London forces and permanent dipole-permanent dipole forces iodine atoms are more polarisable than chlorine or bromine resulting in stronger London Forces so more energy required to overcome these forces. despite 1-iodopropane having the weakest permane |
| what is the order of hydrogen halides of increasing boiling points Lowest------------------------------> Highest A: HF->HCl->HBr->HI B: HI->HBr->HCl->HF C: HCl->HBr->HI->HF D:HF->HI->HBr->HCl | C. HCl--->HBr--->HI--->HF |
| (iii) Explain, with reference to their intermolecular forces, why the boiling temperatures of alkanes increase as the number of carbon atoms increases. A detailed description of the intermolecular forces is not required. (3) | the intermolecular forces are London these forces depend on the number of electrons which increase as the number of carbon atoms increase more energy is needed to break these intermolecular forces so the boiling temperature increases. |
| (iii) Explain, in terms of intermolecular forces, why nitrogen trichloride has a similar boiling temperature to ethanol. | both have london forces london forces are stronger than nitrogen trichloride and because it has 58 electrons whereas ethanol has 26 |
| Q24(a) Urea has a melting temperature of 133 degrees celsius Explain why this value is higher than expected for a relatively small molecule. (3) | Urea forms hydrogen bonds Urea forms permanent dipole-dipole forces these forces are stronger than london forces. |
| 22(d)(i) London forces are present in all of these compounds. Describe how these forces arise. | Instantaneous dipole causes a dipole and in another molecule and these opposite charges attract. |
| (ii) State why the London forces are greater in hydrogen iodide than in hydrogen bromide. (1) | There are 18 more electrons in iodine than bromine |
| 22(d)(iii) Explain why the boiling temperature of hydrogen fluoride is higher than that of hydrogen chloride. (2) | HF also has hydrogen bonds. Hydrogen bonds are stronger than London forces. |
| 23 The boiling temperatures of fluorine and two of its compounds are given below. Substance F2 CH3F HF Tb/K 85 195 293 (a) A molecule of F2 has 18 electrons. Which intermolecular force depends to a large extent on the number of electrons in the molec | London forces |
| (c) Explain why the boiling temperature of CH3F is greater than that of F2, referring to the intermolecular forces present. (1) | Because CH3F has permanent-dipole-dipole attractions also present. |
| (d) Explain why the boiling temperature of HF is the highest in the series.(2) | Hydrogen bonds also present which need more energy to break than dipole-dipole. |
| (e) Explain why the values of the boiling temperatures for Cl2 , CH3Cl and HCl do not follow the same trend as F2, CH3F and HF. (1) | HCl does not have hydrogen bonds between molecules. |
Created by:
mercy2404