I have no clue how to do this, any help? Thanks! An unknown gas, X2(g), which be

Question

I have no clue how to do this, any help?
Thanks! An unknown gas, X2(g), which behaves much like N2(g) (N N), is analysed and the following enthalpies of formation are obtained: We also know that the X-H bond energy is 412 kJ/mol. Use this information to estimate the X-X (single-)bond en­ergy in the X2H4 molecule. Give your answer to the nearest 1 kJ/mol.

Explanation / Answer

H2 => 2H        delH = 2*217- 0 = 434 kJ      (note that Hf forH2 = 0 b/c standard state convention) This means the breaking of H-H bonds costs 434 kJ X2 => 2X        delH = 2*468- 0 = 936 kJ,    because X2 is the standardstate So to break a X-X bond in diatomic X2, need 936 kJ The pertinent reaction is X2 + 2H2 => X2H4 bonds broken: X-X bond and 2 H-H bond del H, broken = 936 + 2*434 = 1806 kJ bonds formed: 4 X-H bonds and 1 X-X bond (note this X-X bond energyis not the same as the one we calculated for diatomic X-X, becausebond energy is dependent on molecular structure; the H have effecton the X-X bond in X2H4) delH, formed = 4*412 + 1*delH_X-X in X2H4 delH broken- delH, formed = -13, the enthalpy of formation ofX2H4 1806- (4*412 + delH_X-X in X2H4) = -13 delH_X-X in X2H4 = 171 kJ

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