Answer:
Information shadow:
(i) \[{{C}_{6}}{{H}_{6}}(l)+\frac{15}{2}{{O}_{2}}(g)\to
6C{{O}_{2}}(g)+3{{H}_{2}}O(l);\]
\[\Delta
H=-3267kJ\]
(ii) \[C(s)+{{O}_{2}}(g)\to
C{{O}_{2}}(g);\,\,\,\,\Delta H=-393.5kJ\]
(iii) \[{{H}_{2}}(g)+\frac{1}{2}{{O}_{2}}(l)\to
{{H}_{2}}O(l);\,\,\,\,\,\Delta H=-285.83kJ\]
The required
equation is:
\[6C(s)+3{{H}_{2}}(g)\to
{{C}_{6}}{{H}_{6}}(l);\,\,\,\,\,\,\,\,\Delta H=?\]
Problem
solving strategy:
The heat of
required equation can be obtained by algebraic method.
(ii) \[\times
\] 6 + (iii) \[\times \] 3 + (i)
Working
it out:
\[6C(s)+6{{O}_{2}}(g)\to
6C{{O}_{2}}(g);\Delta H=-393.5\times 6kJ\]\[3{{H}_{2}}(g)+\frac{3}{2}{{O}_{2}}(g)\to
3{{H}_{2}}(l);\,\,\,\,\Delta H=-285.83\times 3kJ\]\[6C{{O}_{2}}(g)+3{{H}_{2}}O(l)\to
{{C}_{6}}{{H}_{6}}(l)+\frac{15}{2}{{O}_{2}}(g);\,\] \[\Delta H=+3267kJ\]
On
adding,_____________________________
\[6C(s)+3{{H}_{2}}(g)\to
{{C}_{6}}{{H}_{6}}(l);\,\,\,\,\,\,\Delta H=+48.51kJ\,mo{{l}^{-1}}\]Alternatively,
\[6C(s)+3{{H}_{2}}(g)\to {{C}_{6}}{{H}_{6}}(l)\]
\[{{\Delta
}_{r}}H=\sum \]Heat of combustion of reactants
\[-\sum \]
Heat of combustion of products
= 6 x
(-393.5) + 3 (-285.83) - (- 3267)
\[=48.51kJ\,mo{{l}^{-1}}\]
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