Determine enthalpy of formation for `H_(2)O_(2)(l)`, using the listed enthalpies of reaction :
`N_(2)H_(4)(l)+2H_(2)O_(2)(l)toN_(2)(g)+4H_(2)O(l)`,
`" "Delta_(r)H_(1)^(@)=-818kJ//mol`
`N_(2)H_(4)(l)+O_(2)(g)toN_(2)(g)+2H_(2)O(l)`
`" "Delta_(r)H_(2)^(@)=-622kJ//mol`
`H_(2)(g)+(1)/(2)O_(2)(g)toH_(2)O(l)" "Delta_(r)H_(3)^(@)=-285kJ//mol`

Options

A. `-383` kJ/mol
B. `-187` kJ/mol
C. `-498` kJ/mol
D. None of these

Answer

B

Explanation

For `H_(2)(g)+O_(2)(g)rarrH_(2)O_(2)(l)`
`Delta_(f)H^(@)(H_(2)O_(2),l)=Delta_(r )H_(3)^(@)+(Delta_(r )H_(2)^(@))/(2)-(Delta_(r )H_(1)^(@))/(2)`