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Introduction to Enthalpy of Reaction

Enthalpy of reaction (ΔH_rxn) is the heat change that occurs during a chemical reaction at constant pressure.

Key Concepts

  • Exothermic Reactions: Release heat to surroundings (ΔH_rxn < 0)
  • Endothermic Reactions: Absorb heat from surroundings (ΔH_rxn > 0)
  • Standard Conditions: 1 atm pressure and 25°C for measuring ΔH

Calculating ΔH_rxn

  1. Using bond enthalpies:
    ΔH_rxn ≈ Σ(Bonds Broken) − Σ(Bonds Formed)
  2. Using enthalpies of formation:
    ΔH_rxn = Σ ΔH_f°(products) − Σ ΔH_f°(reactants)

Importance

  • Predicts heat released or absorbed in reactions
  • Essential for thermodynamics, chemical engineering, and safety calculations
  • Helps in designing energy-efficient reactions

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