Use the bond enthalpies and bond energies in the data book in themochemical equations to calculate the reaction enthalpy of: H2(g) +Br2(g) -> 2HBr(g)
delta Hrxn = (n*DHf products)-(n*DHfreactants).
n*DH reactants is zero for H2 and zero for Br2.
To calculate the reaction enthalpy of the given thermochemical equation, we need to use the bond energies or bond enthalpies of the bonds involved in the reaction. Bond energies represent the energy required to break the bond, while bond enthalpies represent the energy change associated with breaking a bond in a gaseous molecule, with reactants as gaseous molecules and products also in gaseous form.
Let's look at the bonds involved in the reaction:
H-H (in H2, gaseous state)
Br-Br (in Br2, gaseous state)
H-Br (in HBr, gaseous state)
We can find the bond energies or bond enthalpies for each bond from the data book. Let's assume the bond energies given are:
H-H bond energy = X kJ/mol
Br-Br bond energy = Y kJ/mol
H-Br bond energy = Z kJ/mol
The reaction enthalpy (∆H) can be calculated as follows:
∆H = Σ (bond energies of bonds broken) - Σ (bond energies of bonds formed)
In the given reaction, we break one H-H bond and one Br-Br bond, and form two H-Br bonds.
∆H = (1 * X) + (1 * Y) - (2 * Z)
Substituting the values from the data book, we can calculate the reaction enthalpy.