Chapter 15, Problem 93A

Interpretation Introduction

Interpretation:

The thermochemical equation for conversion of diamond to graphite needs to be explained.

Concept introduction:

TheHess law states that the change of enthalpy in a chemical reaction is dependent only on the initial and final state and not on the intermediate states.

Answer to Problem 93A

The equation for the given reaction is $C(s,diamond)\to C(s,graphite),\Delta H=-2kJ$

Explanation of Solution

Given reactions:

$\begin{array}{l}C(s,graphite)+O_2(g)\to C{O}_2(g),\Delta H=-394kJ\\ C(s,diamond)+O_2(g)\to C{O}_2(g),\Delta H=-396kJ\end{array}$

Subtracting the first equation from the second, we get

$\begin{array}{l}C(s,diamond)+O_2(g)+C{O}_2(g)\to C(s,graphite)+O_2(g)+C{O}_2(g),\Delta H=-396+394kJ\\ C(s,diamond)\to C(s,graphite),\Delta H=-2kJ\end{array}$

Conclusion

The required equation was derived using Hess law.