What is the definition of endothermic reaction and exothermic reaction?

Endothermic reactions are reactions that take in energy. This is usually in the form of heat. An example could be evaporation because heat is being absorbed by water and molecules are moving away from each other.  

Reactions that give off energy to their surroundings, usually in the form of heat, are called exothermic reactions. An example of an exothermic reaction is striking a match. Lighting a match gives out heat.

a gas, having a molecular weight of 13 kg/kmol and a kinematic viscosity of 0.25 cm2/s, flows through a pipe 0.25 m internal diameter and 5 km long at the rate of 0.4 m3/s and is delivered at atmospheric pressure.