If `x_(1),x_(2) and x_(3)` are enthalpies of H-H , O=O and O-H bonds respectively , and `x_(4)` is the enthalpy of vaporisation of water , estimate the standard enthalpy of combustion of hydrogen:

Options

A. `X_(1)+(X_(2))/(2) - 2X_(3) + X_(4)`
B. `X_(1)+(X_(2))/(2) - 2X_(3) - X_(4)`
C. `X_(1)+(X_(2))/(2) - X_(3) + X_(4)`
D. `2X_(3)-X_(1)-(X_(2))/(2) -X_(4)`

Answer

B

Explanation

`H_(2)(g) + (1)/(2)O_(2)(g) rarr H_(2)O(l), DeltaH_("comb")H_(2)`
`DeltaH_("comb")=DeltaH_(H-H)+(1)/(2)DeltaH_(0=0)-2DeltaH_(0-H)-DeltaH_("vap")=x_(1)+(x_(2))/(2)-2x_(3)-x_(4)`