Question

Define endothermic and exothermic changes. Give two examples in each case.

Answer 1

Hint: The term endothermic and exothermic is related with the change in heat. In one of them heat is being absorbed and in the other one the heat is released by the system.

Complete step by step answer:
Endothermic reactions are those reactions in which heat is absorbed, the reactants absorb heat in order to convert themselves into products. The heat can either be absorbed from surrounding or can be provided externally to carry out the reaction. The endothermic reaction decreases the temperature of the system because they cause a cooling effect due to absorption of heat from the surrounding.
Examples of endothermic reactions are melting of ice because we either have to provide energy formelting or the substance takes heat from surrounding, evaporation, cooking and photosynthesis etc.
An exothermic reaction is a reaction in which the energy is released. The energy can be released in the form of light, heat or sound. Since the energy is released hence the system heats up. The temperature of the surroundings increases due to release of heat into the surrounding system.
Combustion is a very good example of exothermic reaction. Neutralization reactions are also
example of exothermic reactions. Some other examples are nuclear fusion and respiration.

Note:
The enthalpy change for the endothermic reaction is positive and the energy is written on the reactant side while writing the chemical equation for an endothermic reaction. The enthalpy change for the exothermic reaction is negative. The energy is written on the product side for an exothermic reaction. Enthalpy is a thermodynamic term that is the measurement of energy.