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🧮 Hess's Law Calculator

Calculate enthalpy changes using multiple reaction steps

Multi-Step Hess's Law

Formation Method

Bond Energy Method

Quick Examples

Load common Hess's Law problems:

Hess's Law Theory & Applications

Hess's Law Statement:

"The total enthalpy change for a reaction is independent of the route taken."

ΔH = sum of all individual step enthalpies

Key Principles:

State Function:

Enthalpy depends only on initial and final states, not the path taken.

Reversibility:

Reversing a reaction changes the sign of ΔH but not its magnitude.

Scaling:

Multiplying coefficients multiplies ΔH by the same factor.

Common Applications:

  • Combustion Analysis: Finding enthalpy of formation from combustion data
  • Indirect Measurements: Calculating ΔH for reactions that can't be measured directly
  • Bond Energy Calculations: Using bond dissociation energies to find reaction enthalpies
  • Formation Enthalpies: Building complex reactions from formation data
  • Industrial Processes: Optimizing reaction conditions and energy requirements

Problem-Solving Strategy:

  1. Write the target reaction clearly
  2. List all given reactions and their ΔH values
  3. Manipulate given reactions (reverse, multiply) to match target
  4. Apply corresponding operations to ΔH values
  5. Add manipulated reactions and their ΔH values
  6. Verify that intermediate species cancel out