Which of the following processes are exothermic and which are endothermic?

a) frost forms on a car window in winter; b) water condenses on a glass of ice water on a humid summer afternoon; c) adding ammonium nitrate to water causes the temperature of the solution to decrease

The reactions in which heat is released are known as exothermic, and the reactions in which heat is absorbed are known as endothermic reactions.

a) Frosting comprises the transformation of water vapors present in the air into frost or ice by discharging energy as during the winters temperature is low. Thus a is an example of the exothermic process.

b) A large concentration of water vapors are present in the air and even the temperature is high on a humid summer afternoon. When the vapors encounter with ice water present in a glass, they get condensed to produce water droplets. The condensation discharges energy, hence b is an example of the exothermic process.

c) The dissolution of ammonium nitrate in water minimizes the temperature of the solution as it is utilizing energy from the surroundings. Thus, c is an example of the endothermic process.

Endothermic reactions are reactions that proceed by the absorption of heat (energy) while exothermic reactions involve a release of energy.

a) Formation of frost on a car window in winter is an exothermic process as heat is liberated when liquid water freezes to form crystals

b) Formation of water condensate on a glass of ice water is an endothermic reaction since heat is absorbed by the cold water from the glass container thereby cooling it.

c) A decrease in the temperature as ammonium nitrate is added to water is an endothermic reaction