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.