Question

What does one mean by exothermic and endothermic reactions? Give examples.

Answer 1

Chemical reactions that release energy in the form of heat, light, or sound are called exothermic reactions.
Example: Mixture of sodium and chlorine to yield table salt
Na(s) + $\frac{1 }{ 2}$ Cl2(s) $→$ NaCl(s) + 411 kJ of 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.
6CO2(g) + 6H2O(l) $\xrightarrow{sunlight}$ sunlight C6H12O6(aq)+ 6O2(g)
(Glucose)