Free Hess's Law Calculator
Apply Hess's Law to calculate the overall enthalpy change by summing enthalpy changes of individual steps in a reaction pathway.
kJ
kJ
kJ
Overall ΔH
-300.0 kJ
Overall ΔH vs ΔH of Step 1
Hess's Law
Principle
ΔH_total = ΔH₁ + ΔH₂ + ΔH₃ + ...
Enthalpy is a state function, so the total enthalpy change depends only on the initial and final states, not the pathway. You can add up enthalpy changes of intermediate steps to find the overall change.
Reverse a reaction: change sign of ΔH. Multiply coefficients: multiply ΔH by the same factor.
Example Calculation
Three-step pathway: Step 1 = -200 kJ, Step 2 = -150 kJ, Step 3 = +50 kJ.
- 01ΔH_total = ΔH₁ + ΔH₂ + ΔH₃
- 02ΔH_total = -200 + (-150) + 50
- 03ΔH_total = -300 kJ
Frequently Asked Questions
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