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Calculate the enthalpy change accompanying the transformation of C (graphite) to C(diamond). Given that the enthalpies of combustion of graphite and diamond are 393.5 and 395.4 kJ mol–1 respectively. |
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Answer» Remember, enthalpy of combustion is always negative we are given (i) C (graphite) + O2 (g) → CO2 (g) ; Δc H° = – 393.5 kJ mol–1 (ii) C (diamond) + O2 (g) → CO2 (g) ; Δc H° = – 395.4 kJ mol–1 We aim at C(graphite) → C(diamond), Δtrans H°= ? Subtracting eqn. (ii) from eqn. (i), we get C(graphite – C(diamond) → 0; Δr H° = – 393.5 – (–395.4) = + 1.9 kJ or C(graphite) → (diamond) ; Δtrans H = + 1.9 kJ |
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