Calculation Of Enthalpy Change For The Conversion Of Graphite To Diamond
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Calculation Of Enthalpy Change For The Conversion Of Graphite To Diamond

Graphite and diamond are two forms of carbon.
The enthalpy change of the combustion of graphite is -393.5 KJ.
The enthalpy change of the combustion of diamond is -395.4 KJ.
The following are the chemical equations:

C(graphite) + O2(g) -------> CO2 ΔH = -393.5 KJ.

C(diamond) + O2(g) -------> CO2 ΔH = -395.4 KJ.

Calculate ΔH for the conversion of graphite to diamond

The strings: S7P6A66 (grouping/interaction - chemical).

The math:
Pj Problem of Interest is of type grouping/interaction (chemical).

First Law Of Thermodynamics: energy is conserved. It is neither created nor destroyed.
System: the space of interest.
Surrounding: the space outside a system
Internal Energy (E) of a system: the sum of all the potential and kinetic energies of all of a system's components.
Change In Internal Energy (ΔE): final internal energy - initial internal energy = Efinal - Einitial.
Pressure-Volume Work (PV): work involved in the expansion or compression of gases. Work in general is denoted by w.
Heat (q): degree of hotness (signifies rise in temperature).
Enthalpy (H): a thermodynamic function that accounts for heat flow in processes that occur at constant pressure and in which only PV work is done on the system or on the surrounding.
Change In Enthalpy (ΔH): heat gained or lost by a system at constant pressure.

ΔE = q + w
Where q denotes heat and w denotes work. When heat is transferred to a system, q is positive. When the system loses heat, q is negative. When wrrk is done on the system, w is positive. When work is done by the system, w is negative.

ΔH = ΔE + PΔV = qp
qp = heat lost or gained. The subscript p, implies constant pressure.

Problem is solved using Hess' Law: If a reaction is carried out in a series of steps, ΔH for the overall reaction will equal the sum of the enthalpy changes for the individual steps.

Now the steps for the conversion of graphite to diamond are:

C(graphite) + O2(g) -------> CO2 ΔH = -393.5 KJ.
CO2 -------> C(diamond) + O2(g) - ΔH = 395.4 KJ.

Note that the combustion of diamond to give carbon dioxide has been reversed. Its enthalpy changed becomes negative. So the two equations can be added.
The addition of the two equations produces:

C(graphite) -------> C(diamond) ΔH = 395.4 - 393.5 = 1.9 KJ.
So, ΔH for the conversion of graphite to diamond = 1.9 KJ (KiloJoules).

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