1. Tardigrade
  2. Question
  3. Chemistry
  4. The standard enthalpies of combustion of C6H6, C(graphite) and H2(g) are respectively -3270 kJ mol-1 , -394 kJ mol-1 and -286 kJ mol-1. What is the standard enthalpy of formation of C6 H6(l) in kJ mol-1 ?

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Q. The standard enthalpies of combustion of $C_6H_6, C_{(graphite)}$ and $H_2{(g)}$ are respectively $-3270\, kJ$ $mol^{-1}$ , $-394\, kJ \,mol^{-1}$ and $-286\, kJ\, mol^{-1}$. What is the standard enthalpy of formation of $C_6 H_6(l)$ in $kJ\, mol^{-1}$ ?

KEAMKEAM 2012Thermodynamics

Solution:

On inverting Eq. (i), we get

$6 CO _{2}+3 H _{2} O \longrightarrow C _{6} H _{6}+\frac{15}{2} O _{2} $

$\Delta H=+3270 \,kJ \,mol ^{-1}$

Addition of Eq. (iv), (v) and (vi) gives

$6 C ( s )+3 H _{2} \longrightarrow C _{6} H _{6}$

$\Delta H =+3270+(-2364-858) $

$=+48 \,kJ \,mol ^{-1}$

Thus, the standard enthalpy of formation of

$C _{6} H _{6},\left(\Delta_{f} H_{ C _{6} H _{6}}\right)$ is $+48 \,kJ\, mol ^{-1}$