The hydrogen halides are gases at room temperature. For example, chlorine reacts with hydrogen: The halogens react with hydrogen to produce compounds called hydrogen halides. Reveal answerĢFe(s) + 3Cl 2 (g) → 2FeCl 3 (s) Reactions with hydrogen Write a balanced equation for the reaction of iron with chlorine to produce solid iron(III) chloride,įeCl 3. Hot iron wool reacts slowly in iodine vapour to produce grey iron(II) iodide Hot iron wool burns quickly to produce red-brown iron(III) bromide Hot iron wool burns vigorously to produce orange-brown iron(III) chloride HalogenĬold iron wool burns to produce white iron(III) fluoride The table describes what is seen when halogens react with iron wool.
The halogens become less reactive going down group 7. Sodium and chlorine react vigorously when heated, giving an orange flame and clouds of white For example, chlorine reacts with sodium: The halogens react with metals to produce salts (the word 'halogen' means 'salt former'). This means that the halogens all have similar chemical properties. Diluting the starting products with an inert gas or absorbing the reaction heat with copper granulate can help in this case.Atoms of group 7 elements all have seven electrons in their outer shell. Nevertheless, methane fluorination may be carried out in a controlled reaction, so as to prohibit an explosion. The reaction heat cannot be eliminated from the reaction mixture quickly enough with the consequence that the temperature and thus the reaction rate steadily increase. In addition, chain propagation is extremely exothermic. Therefore, they occur often enough in the reaction mixture, even if placed only at room temperature. In the case of methane fluorination, activation energies of the reactions of chain propagation are small (see also "Early and late transition states"). Otherwise, the reactive radicals formed by the initiation reaction will recombine rather than chain propagation will happen. The activation energy of a chain reaction must not be too high. As a result, the reaction itself provides enough energy for additional initiation reactions. In addition, fluorination is very exothermic, the reaction enthalpy is -431 kJ/mol. Therefore, one start reaction may initiate thousands of fluorination reactions. The subsequent reactions (chain propagation) between a halogen radical and methane, and then between a methyl radical and a halogen molecule, yield another halogen radical. The initial reaction (chain initiation) - that is, the homolytic cleavage of a halogen molecule - must, however, occur only a few times. Therefore, the kinetics of methane halogenation can be illustrated effortlessly.įluorination (155 kJ/mol) seems to have relatively high activation energy. The dissociation energies of all halogens are known. The activation energy of methane halogenation is equivalent to the dissociation energy of the respective halogen, as the halogenation is a gas-phase reaction with a homolytic bond breakage. Therefore, the thermodynamics of methane halogenation are, first of all, determined by the reaction enthalpy (ΔH°). The reaction entropy of methane halogenation is approximately zero, since two molecules of gaseous products are formed from two molecules of gaseous starting products in the reaction. Iodine, on the other hand, does not react with methane. The reaction between methane and chlorine is easily controllable, while bromine is even less reactive than chlorine. If no precautions are taken, a mixture of fluorine and methane explodes. The reactions of fluorine, chlorine, bromine, and iodine with methane are quite differently vigorous.
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