Question

calculate the enthalpy change in the conversion of 10 g graphite in diamond if the heat of combustion of carbon (graphite) and diamond is -94.05 and -94.5 kcal respectively ​

Answer 1

Answer:

The enthalpy change in the conversion of 10 g graphite in diamond is 0.375 kcal.

Explanation:

$C(graphite)(s)+O_2(g)\rightarrow CO_2(g),\Delta H_1=-94.05 kcal/mol$..[1]

$C(diamond)(s)+O_2(g)\rightarrow CO_2(g),\Delta H_2=-94.5 kcal/mol$..[2]

$C(graphite)(s)\rightarrow C(diamond)(s),\Delta H_3=-?$..[3]

Using Hess's law:

[1] - [2] = [3]

$\Delta H_3=\Delta H_1-\Delta H_2=-94.05 kcal/mol - (-94.5 kcal/mol)$

$\Delta H_3=0.45 kcal/mol$

Heat required to change 1 mole of graphite into diamond = 0.45 kcal/mol

Moles of graphite in 10 grams of graphite = $\frac{10 g}{12 g/mol}=0.83333 mol$

Heat required to change 0.83333 mole of graphite into diamond :

0.83333 mol × 0.45 kcal/mol = 0.375 kcal

The enthalpy change in the conversion of 10 g graphite in diamond is 0.375 kcal.