Question

What are examples of Exothermic and Endothermic reactions?

Answer 1

Hint: All the chemical reactions involve energy production. It is required to break the bonds between the reactants and form new ones if needed for formation of products. Some chemical reactions are called exothermic and some are termed as endothermic reactions.

Complete answer:
In an exothermic reaction, there is more energy released when new bonds are formed in the products. The opposite is an endothermic reaction, here it takes more energy to break bonds in the reactant than required in the formation of products. $ \Delta H $ is represented with a positive sign.
Endothermic reactions:
 $ {\text{Reactants + Energy}} \to {\text{ Products}} $
The example of endothermic reaction is photosynthesis. In Photosynthesis, plants form glucose from the reactants carbon dioxide and water respectively. They also release oxygen in the reaction.
The following is the reaction of photosynthesis:
 $ 6C{O_2} + 6{H_2}O \to {C_6}{H_{12}}{O_6} + 6{O_2} $ .
 Plants that perform photosynthesis get light from the sun. Without this, photosynthesis cannot occur.
Exothermic reactions: In exothermic reactions, there is more energy released when new bonds are formed in the products, than the energy required in breaking the bonds of reactant. The following is the reaction.
 $ {\text{Reactants }} \to {\text{ Products + Energy}} $
There is always a rise in temperature in exothermic reactions. $ \Delta H $ is represented with a negative sign.
The classic example of exothermic reaction is combustion. During combustion reactions, a substance burns as it combines with oxygen. When a substance burns, they usually give off energy as heat and light.

Note:
Combustion of wood is an example of exothermic reaction that releases a lot of energy as heat and light. You can see the light energy the fire is given off. If you were standing near the fire, you would also feel its heat.