Explanation:
The reaction equation will be as follows.

Using bond energies, expression for calculating the value of
is as follows.

On reactant side, from
number of bonds are as follows.
C-C bonds = 1
C-H bonds = 6
From
; Cl-Cl bonds = 1
On product side, from
number of bonds are as follows.
C-C bonds = 1
C-H bonds = 5
C-Cl bonds = 1
From HCl; H-Cl bonds = 1
Hence, using the bond energies we will calculate the enthalpy of reaction as follows.

=
= -102 kJ/mol
Thus, we can conclude that change in enthalpy for the given reaction is -102 kJ/mol.
In a data table, units of measurement should be shown in the headings of
columns. The unit of measurement would appear first fully spelled out
(for example, Watt) and then an abbreviated version to be used in the
data will come afterwards, either after a forward slash or within
brackets (for example, /w or (w)).