Question

`C_(("graphite"))+O_(2)(g)rarrCO_(2)(g), DeltaH=-94.05 kcal mol^(-1)`
`C_(("diamond"))+O_(2)(g)rarrCO_(2)(g), DeltaH=-94.50 kcal mol^(-1)` therefore
A. `C_(("graphite"))rarrC_(("diamond")), DeltaH_(298 K)^(@)=-450 cal mol^(-1)`
B. `C_(("diamond"))rarrC_(("graphite")), DeltaH_(298 K)^(@)=+450 cal mol^(-1)`
C. Graphite is the stabler allotrope
D. Diamond is harder than graphite

Answer 1

Correct Answer - C
Heat energy is also involved when one allotropic form of an element in to another. Graphite is the stabler allotrope because the heat of transformation of
`C_(("diamond"))rarrC_(("graphite"))`.
(i) `C_(("dia"))+O_(2)(g)=CO_(2(g))DeltaH=-94.5 kcal`
(ii) `C_(("graphite"))+O_(2(g))=CO_(2(g))DeltaH=-94.0 k cal`
`DeltaH_("transformation")=-94.5-(-94.0)`
`=-0.5 kcal`.