1. 14.2 Energy and Chemical Reactions
Energy is transferred in chemical reactions in two ways:
to break some (or all) chemical bonds between atoms in the reactants
To form new chemical bonds to make new products.

2. Two Types of Energy Transfers
We classify chemical reactions based on how the energy is transferred between the reactants and the products.
Endothermic – Heat is absorbed by the reactants during the reaction (“In”). Examples: Cold Pack, Photosynthesis
Exothermic – Heat is released by the reactants during the reaction (“Exit”). Examples: Heating Pack, Burning fossil fuels

3. Energy is also Transferred in Physical Changes (recall phase changes) Exothermic:
Condensation of water vapor to liquid rain
Freezing of water to ice
Deposition of water vapor to frost
Endothermic:
Vaporization of liquid water to steam
Melting of ice to liquid water
Sublimation of dry ice (CO2) to vapor