Question

Calculate $\Delta H$ (in Joules) for, $C$ (graphite) $\rightarrow C$ (diamond), from the following data $C ($ graphite $)+ O _{2}(g) \rightarrow CO _{2}(g) ; \Delta H =-393.5\, kJ\, C$ (diamond) $+ O _{2}(g) \rightarrow CO _{2}(g) ; \Delta H =-395.4\, kJ$

• A. $ 1,900 $
• B. $ -788.9\times 10^{3} $
• C. $ 1,90,000 $
• D. $ +\,788.9\times \,10^{3} $

Answer 1

Answer: (A)

$C$ (graphite) $+ O _{2}(g) \rightarrow CO _{2}(g)$
$\Delta H =-393.5 \,kJ .$..(i)
$C$ (diamond) $+ O _{2}(g) \rightarrow CO _{2}(g)$
$\Delta H =-395.4\, kJ$..(ii)
$C$ (graphite) $\rightarrow C$ (diamond);
Subtract the Eq (ii) form (i)
$C$ (graphite) $\rightarrow C$ (diamond)
$\Delta H=-393.5-(-395.4)$
$=1.9\, k J=1900 \,J$