EK Chemistry 30 Min Exam, Lecture 1, Q 14.

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Sterling Archer

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Jun 13, 2012
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Hello everyone,

Can anyone explain why the answer for this question is A? The solution manual says simply substitute H for X in the equation for delta, but I don't understand how that becomes 0.

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The equation for expected bond energy is give as

expected bond energy = 1/2( (H-H) + (X-X))

Substitute in H for X

expected bond energy = (1/2) (H-H +H-H) = bond energy of H-H

Substitute expected bond energy into the first equation

delta = (H-H) - (H-H) = 0

Basically, the second equation means that the expected bond energy is calculated with reference to the bond energy of H-H. And since our element of interest happens to also be hydrogen, it follows that electronegativity is zero.