If x1, x2 and x3 are enthalpies H−H,O=O and O−H bonds respectively, and x4 is the enthalpy of vaporization of water. Estimate the standard enthalpy of combustion of hydrogen.
A
x1+x22−2x3+x4
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B
x1+x22−2x3−x4
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C
x1+x22−x3+x4
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D
2x3−x1−x22−x4
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Solution
The correct option is Bx1+x22−2x3−x4 Combustion of hydrogen: H2+12O2→H2O(H−O−H)
As water contains two O−H bonds.
So, combustion enthalpy of hydrogen is:
ΔH= Bond energy of reactant − Bond energy of the product − Enthalpy of vapourisation.