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The combusition of 1 mol of benzene (C(6...

The combusition of 1 mol of benzene `(C_(6) H_(6))` takes place at `298 K` and 1 bar pressure. After combustion, `CO_(2) (g)` and `H_(2) O (1)` are produced and `3267 kJ` of heat is liberated. Calculate the standard enthaply of formation, `Delta_(f) H^(@)` of benzene. Standard enthapies of formation of `CO_(2) (g)` and `H_(2) O (1)` are `- 393.5 kJ mol^(-1)` and `- 258.83 kJ mol^(-1)`, respectively.
Strategy : Apply Eq. the mathematical form of Hesis's law, to the combustion reaction of 1 mol of benzene. Remember `Delta_(f) H^(@)` for `O_(2) (g)` is zero by convention. We are give `Delta_(1) H^(@)` and `Delta_(f) H^(@)` values for all substance except `C_(6) H_(6) (1)`. We can solve for this unknown.

Text Solution

Verified by Experts

The thermochemical equation for the combustion of one mole of benzene is:
`C_(6) H_(6) (1) + (15)/(2) O_(2) (g) rarr 6 CO_(2) (g) + 3 H_(2) O (1)`,
`Delta_(C ) H^(@) = - 3267 kJ mol^(-1)`
Applying Eq. we can write
`Delta_(C )H^(@)=[(6 mol CO_(2),g)Delta_(C )H^(@)(CO_(2),g)+(3mol H_(2)O,l)Delta_(f)H^(@)(H_(2)O,l)]-[(1 mol C_(6)H_(6))Delta_(f)H^(@)(C_(6)H_(6),l) + (15//2 mol O_(2), g) Delta_(f) H^(@) (O_(2), g) - 3267`
`= [(6) (-393.5) + (3) (-285.83)] - [Delta_(f) H^(@) (C_(6) H_(6), g) + 0]`
Rearranging to solve for `Delta_(f) H^(@) (C_(6) H_(6), g)`,we have
`Delta_(f) H^(@) (C_(6) H_(6), g) = (3267) - (2361) - (857.49)`
`= 48.51 kJ mol^(-1)`
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The combustion of 1 mole of benzene takes placeat 298K and 1 atm. After combustion, CO_(2)(g) and H_(2)O(l) are produced and 3267.0kJ of heat is liberated. Calculate the standard enthalpy of formation, Delta _(f) H^(@) of benzene. Standard enthalpies of formation of CO_(2)(g) and H_(2)O(l) are -393.5kJ mol^(-1) and -258.83kJ mol^(_1) respectively

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Knowledge Check

  • The standard enthalpy of formation of octane (C_(8)H_(18)) is -250 KJ/mol. Calculate the enthalpy of formation of CO_(2)(g) and H_(2)O_(l) are -394 KJ/mol and -286 KJ/ mol respectively :

    A
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    B
    -5726 KJ/mol
    C
    -5476 KJ/mol
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    -5310 KJ/mol

  • If the heats of formation of C_(2)H_(2) and C_(6)H_(6) are 230 kJ mol^(-1) and 85 kJ mol^(-1) respectively, the DeltaH value for the trimerisation of C_(2)H_(2) is

    A
    `-605 kJ`
    B
    `-205 kJ`
    C
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  • The enthalpies of formation of CO and CO_(2) are -110.5 KJ mol^(-1) and -393.5 KJ mol^(-1) respectively. The enthalpy of combustion of carbon monoxide is

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    `-283.0 KJ mol^(-1)`
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    `221.2 KJ mol^(-1)`

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