A) \[{{C}_{2}}{{H}_{2}}+2{{H}_{2}}\to {{C}_{2}}{{H}_{6}};\,\,\Delta E=-314.0\,kJ\]
B) \[C+{{O}_{2}}\to C{{O}_{2}};\,\,\Delta E=-393.5\,kJ\]
C) \[{{N}_{2}}+{{O}_{2}}\to 2NO;\,\,\Delta E-180.5\,kJ\]
D) \[2{{H}_{2}}+{{O}_{2}}\to 2{{H}_{2}}O;\,\,\Delta E+571.8\,kJ\]
Correct Answer: C
Solution :
Heats of combustions are always exothermic except oxidation of N as, \[{{N}_{2}}+\frac{1}{2}{{O}_{2}}\to {{N}_{2}}O\]\[\Delta H=+\,ve\] \[{{N}_{2}}+{{O}_{2}}\,\to 2NO\] \[\Delta H=+\,ve\]
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