Because known compounds with O-Br bonds tend to be unstable, there are no thermo

Question

Because known compounds with O-Br bonds tend to be unstable, there are no thermodynamic data available with which to calculate the O-Br bond enthalpy. However, we can estimate a value from Pauling’s formula relating electronegativities and bond enthalpies:

BE(A-B) = 1/2[BE(A-A) + BE(B-B)] + k(XA - XB)2

Here XA and XB are the electronegativities of atoms A and B, and k is a constant equal to 98.6 kJ.
Using Pauling’s electronegativities and the bond enthalpies given in the following table, calculate the O-Br bond enthalpy.

BEO-Br = ??? kJ/mol

Explanation / Answer

O=O bond enthalpy is 495 Kj/mol

Br-Br bond enthalpy is 193 Kj/mol

Electro negativity of Br is 2.96

Electro negativity of O is 3.44

Pauling’s formula relating electronegativities and bond enthalpies:

BE(A-B) = 1/2[BE(A-A) + BE(B-B)] + k(XA - XB)2

BE(O-Br) = 1/2[BE(O=O) + BE(Br-Br)] + k(XO - XBr)2

  BE(O-Br) = 1/2[495 + 193] + 98.6(3.44 -2.96)^2

BE(O-Br)   = 344 +22.72

BE(O-Br)   = 366.72 Kj/mol

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