What is the enthalpy of reaction, ΔH, for the formation of tungsten carbide, WC, from its
elements?
W (s) + C (graphite) → WC (s)
The enthalpy change for this reaction is difficult to measure directly, because the reaction
occurs at a very high temperature
. However, we can calculate an approximate value for the enthalpy of reaction using standard enthalpies of formation.
The standard enthalpy of formation of tungsten carbide (WC) is -96.8 kJ/mol, the standard enthalpy of formation of carbon in graphite form (C) is 0 kJ/mol, and the standard enthalpy of formation of tungsten (W) is 0 kJ/mol.
Using Hess's Law, we can write the enthalpy of reaction as:
ΔH = ΣnΔHf(products) - ΣnΔHf(reactants)
ΔH = (-96.8 kJ/mol) - (0 kJ/mol + 0 kJ/mol)
ΔH = -96.8 kJ/mol
Therefore, the enthalpy of reaction for the formation of tungsten carbide from its elements is approximately -96.8 kJ/mol.