Posted by **Jude** on Monday, December 13, 2010 at 4:33pm.

Consider the hypothetical elements X and Y. Suppose the enthalpy of formation for the compound XY is -336 kJ/mol, the bond energy for X2 is 414 kJ/mol, and the bond energy for Y2 is 159 kJ/mol. Estimate the XY bond energy in units of kJ/mol.

- chemistry -
**DrBob222**, Monday, December 13, 2010 at 4:52pm
I worked this for you earlier but I wasn't sure if the delta Hf was -336 or not. It is; therefore, the delta Hrxn is -672 for the reaction as written.

X2 + Y2 ==> 2XY

(sum B.E.X2 + B.E.Y2)-(sum B.E. 2XY) = deltaHrxn*2

(414+159)-(2*XY) = -672

Solve for XY and I get 622.5 kJ/mol for X-Y.

Check that this way:

(1/2)X2 + (1/2)Y2 = XY

(sum B.E.X2 + B.E.Y2)-(B.E.XY) = ??

(207+79.5)-(622.5) = ??

(286.5)-(622.5) = -336

Check my thinking.

- chemistry -
**a**, Thursday, November 8, 2012 at 9:42pm
Consider hypothetical elements X and Y. Suppose the enthalpy of formation of the compound XY is −336 kJ/mol, the bond energy for X2 is 421 kJ/mol, and the bond energy for Y2 is 152 kJ/mol. Estimate the XY bond energy in units of kJ/mol.

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