Thermochemistry

Thermochemistry

Overview

Thermochemistry is the study of heat energy changes that occur during chemical reactions and physical transformations. It bridges chemistry and thermodynamics, focusing on the energy flow between chemical systems and their surroundings.

Key Concepts

Enthalpy (H)

• Heat content of a system at constant pressure

• ΔH = heat absorbed or released during a reaction

• Exothermic reactions: ΔH < 0 (release heat)

• Endothermic reactions: ΔH > 0 (absorb heat)

Hess's Law

• Total enthalpy change is independent of pathway

• Allows calculation of ΔH for reactions that can't be measured directly

• ΔH_total = Σ ΔH_steps

Standard Enthalpy Changes

• Formation (ΔH°f): Making 1 mole from elements

• Combustion (ΔH°c): Complete burning in oxygen

• Solution (ΔH°sol): Dissolving in solvent

• Fusion/Vaporization: Phase transitions

Applications

• Calorimetry: Measuring heat changes experimentally

• Bond energies: Estimating reaction energies

• Industrial processes: Optimizing energy efficiency

• Biochemistry: Understanding metabolic pathways

Fundamental Equation

ΔH°reaction = Σ ΔH°f(products) - Σ ΔH°f(reactants)

Thermochemistry provides the quantitative framework for understanding energy in chemical processes, essential for everything from designing batteries to understanding metabolism.