Question

What is the enthalpy change for the process $C(graphite) \to C(g)$ called?
(This question has multiple correct options)
(A) Heat of vaporization
(B) Heat of sublimation
(C) Heat of allotropic change
(D) Heat of atomization

Answer 1

Hint: In thermodynamics, the term enthalpy change is used to denote the amount of heat absorbed or the amount of heat evolved in a chemical reaction at a constant pressure.

Complete step by step answer: The given reaction is $C(graphite) \to C(g)$
We need to find out the name of the enthalpy change for this reaction process.
There are many allotropes of carbon, i.e., there are many forms of carbon which are structurally different. Out of these allotropes of carbon, graphite and diamond are the most well-known. Also, graphite is considered to be the most stable allotrope of carbon.
Now, from the given reaction process we can see that the reactant side has graphite which is in solid state while the product side has carbon in the gaseous state. This means the process involves the conversion of solid into the vapor state or gaseous state without undergoing transformation into the intermediate liquid state.
Now let us consider the first option which is heat of vaporization. Heat of vaporization is also known as enthalpy of vaporization or heat of evaporation and this term is used to denote the amount of heat or energy added to a liquid substance to transform it into gas. So this enthalpy change does not define the given reaction process. So option (A) is not correct.
Let us consider the second option which is heat of sublimation. Heat of sublimation is also known as enthalpy of sublimation and it refers to the amount of heat needed to convert one mole of a substance from solid to gaseous state at constant pressure without undergoing the liquid phase. Therefore, this enthalpy change defines the given reaction and so option (B) is correct.
Since the given reaction involves the conversion of one allotrope of carbon into another allotrope, the enthalpy change involved is the heat of allotropic change. So, option (C) is also correct.
Since heat of atomization refers to the change in enthalpy when one mole of bonds breaks completely to give gaseous atoms, hence option (D) is not correct.
So there are two correct options which are option (B) and option (C).

Note: The enthalpy of a reaction is called the standard enthalpy if all the reactants and products are in their standard states.