Question

The enthalpy changes to make a diamond from graphite are $1.88{\text{kJmol}}^{-1}$. Which gives off more heat when a burned-a pound of diamonds or a pound of graphite? Explain.

Short answer

The burning of diamonds will produce more heat.

Step-by-step solution

Given data

The enthalpy change from graphite to diamond is $1.88\text{kJ}/\text{mol}.$

Concept of the Hess law

The overall enthalpy change throughout a full chemical reaction is the same regardless of the path taken by the chemical reaction, as per Hess's law.

Representation of Hess law

The reaction of combustion of the diamond is written as:

${\text{C}}_{s,\text{diamond}}+{\text{O}}_2={\text{C}}_{s,\text{graphite}}+{\text{O}}_2+\Delta H_{\text{conversion}}$

The product would then be:

${\text{CO}}_2+\Delta H_{\text{conversion}}+\Delta H_{\text{graphite}}$

This means that the enthalpy of diamond burning is more negative than the combustion of graphite because the enthalpy change of diamond to graphite is negative.

Structure of diamond and graphite

Diamond has a 3-D tetrahedral structure and graphite- has a 2-D layered structure.

Diamond has more covalent bonds in its structure, it will release more energy as compared to that of graphite.

Therefore, the burning of the diamond will produce more heat.