Energy-Energy and Chemical Bonding
A chemical reaction is a process of breaking and bond formation. The process is always accompanied by energy changes. The energy required to break chemical bonds, thus forming free radicals called the bond energy. For complex molecules, the energy required to break the molecule to form free atoms called atomization energy.
Atomization energy prices is the amount of the bond energy of the atoms in the molecule. For covalent molecule consisting of two atoms such as H 2, 0 2, N 2 or HI which has a bond equal to the energy of atomization energy bond energy of atomization of a compound can be determined by the help enthalpy of formation of these compounds. Mathematically it can be described by the equation:
ΔH reaction = No. of bond breaking energy - energy Qty bond formation
= No. of bond energy on the left - No. of bond energy on the right
example:
Given:
bond energy
C - H = 414.5 kJ / mole
C = C = 612.4 kJ / mol
C - C = 346.9 kJ / mol
H - H = 436.8 kJ / mol
asked:
ΔH reaction = C 2 H 4 (g) + H 2 (g) → C 2 H 6 (g)
chemical-sma_001
ΔH reaction = Total bond breaking energy - amount of energy bond formation
= (4 (C-H) + (C = C) + (H-H)) - (6 (C-H) + (C-C))
= ((C = C) + (H-H)) - (2 (C-H) + (C-C))
= (612.4 + 436.8) - (2 x 414.5 + 346.9)
= - 126.7 kJ
