Hess's Law Calculator Formula
Understand the math behind the hess's law calculator. Each variable explained with a worked example.
Formulas Used
Overall ΔH
delta_h_total = delta_h1 + delta_h2 + delta_h3Variables
| Variable | Description | Default |
|---|---|---|
delta_h1 | ΔH of Step 1(kJ) | -200 |
delta_h2 | ΔH of Step 2(kJ) | -150 |
delta_h3 | ΔH of Step 3 (0 if none)(kJ) | 50 |
How It Works
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.
Worked Example
Three-step pathway: Step 1 = -200 kJ, Step 2 = -150 kJ, Step 3 = +50 kJ.
delta_h1 = -200delta_h2 = -150delta_h3 = 50
- 01ΔH_total = ΔH₁ + ΔH₂ + ΔH₃
- 02ΔH_total = -200 + (-150) + 50
- 03ΔH_total = -300 kJ
Ready to run the numbers?
Open Hess's Law Calculator