Select the type of bonds involved in the reaction or input the bond energies manually.
Input the number of bonds broken in the reactants.
Input the number of bonds formed in the products.
Click "Calculate Energy" to determine the net energy change (ΔH).
The calculator will display detailed steps of the calculations.

The energy change (ΔH) for a chemical reaction is calculated as:

ΔH = Σ(Bond Energies of Bonds Broken) - Σ(Bond Energies of Bonds Formed)

Where:

Consider the reaction: 2H₂ + O₂ → 2H₂O
Bonds broken: 2 × (H–H) + 1 × (O=O)
Bonds formed: 4 × (O–H)
Using bond energies:

ΔH = [2(436) + 498] - [4(463)] = (872 + 498) - 1852 = 1370 - 1852 = -482 kJ/mol

This negative value indicates the reaction is exothermic, releasing energy in the form of heat.

Reaction: N₂ + 3H₂ → 2NH₃
Bonds broken: 1 × (N≡N) + 3 × (H–H)
Bonds formed: 6 × (N–H)

ΔH = [945 + 3(436)] - [6(391)] = (945 + 1308) - 2346 = 2253 - 2346 = -93 kJ/mol

This shows that ammonia formation releases energy, which is why it is energetically favorable under controlled conditions.

Fuel efficiency and combustion: Engineers calculate energy released in fuels like gasoline, hydrogen, and natural gas.
Industrial chemical production: Processes like the Haber process or the production of sulfuric acid rely on energy balance calculations.
Environmental chemistry: Bond energies help estimate energy changes in atmospheric reactions, including ozone depletion and greenhouse gas formation.
Biochemistry: Understanding energy changes in metabolic reactions helps explain how cells generate ATP and perform work.
Material science: Predicting stability and reactivity of polymers and new materials relies on bond strength estimates.

Bond energies are average values, so results are approximate.
This method assumes all species are in the gas phase. Condensed-phase reactions may vary.
ΔH calculated using bond energies may differ slightly from experimental values due to molecular geometry and resonance.
Always confirm bond types and count accurately for correct results.