Chemical reactions that release energy in the form of heat, light, or sound are called
Example: Mixture of sodium and chlorine to yield table salt
C (g) + O2 (g) → CO2 + Heat Energy
In other words, combination reactions are exothermic.
Reactions that absorb energy or require energy in order to proceed are called endothermic reactions.
For example: In the process of photosynthesis, plants use the energy from the sun to
convert carbon dioxide and water to glucose and oxygen. or