The most important exception to remember for electron gain enthalpy is that period 3 p-block elements (like Si, P, S, Cl) have more negative \(\Delta_{eg}H\) than their corresponding period 2 counterparts (C, N, O, F). This single fact is often the key to solving matching questions involving these elements.
To solve the problem of matching the given elements with their correct electron gain enthalpy values, let's analyze the data from the question:
The table provides the electron gain enthalpies (\(\Delta_{eg}H\)) for various elements. The correct matching is determined by the electron gain enthalpy value associated with each element.
Element O (Oxygen): Oxygen has a mid-range electron gain enthalpy compared to elements like F and Cl. The most appropriate value here is -141 kJ/mol. Therefore, Oxygen corresponds to III.
Element F (Fluorine): Fluorine has the highest electron gain enthalpy of this set, making it very reactive in terms of gaining an electron. The value of -328 kJ/mol is closest to expectations for Fluorine. Hence, Fluorine corresponds to IV.
Element Cl (Chlorine): Chlorine often shows very high electron gain enthalpy as well but typically less than Fluorine. Here, the value is -349 kJ/mol, which is a perfect fit. So, Chlorine corresponds to II.
Element S (Sulfur): Sulfur has a lower electron gain enthalpy characteristic compared to the others listed here. The correct value is -200 kJ/mol. Therefore, Sulfur corresponds to I.
According to the pairings described:
A-III (Oxygen: -141 kJ/mol)
B-IV (Fluorine: -328 kJ/mol)
C-II (Chlorine: -349 kJ/mol)
D-I (Sulfur: -200 kJ/mol)
Therefore, the correct answer is A-III, B-IV, C-II, D-I.
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