Thermochemistry and Energy Changes

## How Energy Flows in Reactions Thermochemistry studies the energy changes during chemical reactions, especially heat flow. Energy can be absorbed (endothermic) or released (exothermic). ### Key Concepts - **Enthalpy (\( \Delta H \))**: The heat content of a system at constant pressure. - **Exothermic Reaction:** Releases energy (\( \Delta H < 0 \)). - **Endothermic Reaction:** Absorbs energy (\( \Delta H > 0 \)). ## Calculating Energy The change in enthalpy can be measured with a calorimeter. \[ q = m \times c \times \Delta T \] where \( q \) is heat, \( m \) is mass, \( c \) is specific heat, and \( \Delta T \) is temperature change. ## Chemical Energy in Life - Hand warmers use exothermic reactions to generate heat. - Photosynthesis is an endothermic process that stores energy from sunlight.