Q. 24 B 5.0( 1 Vote )

(i) Compare the oxidizing action of and by considering parameters such as bond dissociation enthalpy, electron gain enthalpy and hydration enthalpy.

(ii) Write the conditions to maximize the yield of by contact process.

(iii) Arrange the following in the increasing order of property mentioned:

A. (Reducing character)

B. (Base strength)

Answer :

(i) Oxidising power depends on factors like bond dissociation enthalpy, electron gain enthalpy and hydration enthalpy. The electron gain enthalpy of fluorine is less negative than that of chlorine and since fluorine has smaller size, it has higher hydration enthalpy as compared to chlorine. In case of fluorine, because of its small size, it faces greater inter electronic repulsion among its lone pairs of electrons, whereas there is very less repulsion in chlorine. Therefore, the bond dissociation enthalpy of fluorine is lower than that of chlorine. The resultant of all the above factors results in a higher oxidizing power of fluorine.

(ii) One of the key steps to manufacture sulphuric acid via the contact process is the conversion of SO2 to SO3 using V2O5 as a catalyst. Since this reaction is exothermic in nature and the ratio of the gaseous reactants to gaseous products is 2:1, thus according to the Le Chatilier’s principle, to obtain the maximum amount of SO3, low temperature and high pressure are required.

(iii) A. Reducing character: H3PO4 < H3PO3 < H3PO2

B. Basic Strength: BiH3 < SbH3 < PH3 < NH3

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