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) + \(\frac{1 }{ 2}\) Cl_2(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.
6CO_2(g) + 6H₂O_(l) \(\xrightarrow{sunlight}\) sunlight C₆H₁₂O_6(aq)+ 6O_2(g)
                                                                (Glucose)