Hess's Law Calculator

Calculate reaction enthalpy using Hess's Law

Hess's Law Calculator

Target Reaction

Known Reactions

Hess's Law:

• ΔH is state-independent: The enthalpy change depends only on initial and final states
• Additive property: ΔH(total) = ΔH₁ + ΔH₂ + ΔH₃ + ...
• Reversing reactions: ΔH(reverse) = -ΔH(forward)
• Multiplying reactions: ΔH(n × reaction) = n × ΔH(reaction)

Example:

Target: C(s) + O₂(g) → CO₂(g)
Given reactions:
1. C(s) + ½O₂(g) → CO(g) ΔH = -110.5 kJ/mol
2. CO(g) + ½O₂(g) → CO₂(g) ΔH = -283.0 kJ/mol
Solution: Add reactions 1 + 2 = -393.5 kJ/mol