Question

Fill in the blanks:
The reaction in which energy is evolved is called ________.

Answer 1

Hint: As we know that a chemical reaction is a process in which one or more substances, the reactants, are converted to one or more different substances, the products. Substances are either chemical elements or compounds. A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products.

Complete step by step answer:
We have to remember that all chemical reactions involve energy changes. In some reactions, we are able to observe these energy changes as either an increase or a decrease in the overall energy of the system. In some reactions we see this as a change in the temperature. In other reactions we can observe this change when a reaction starts to give off light or when a reaction will only work after light is shone on it.
Now, we need to understand two important concepts i.e. exothermic and endothermic reactions.
An exothermic reaction is that it is one in which the energy of the products is less than the energy of the reactants, because energy has been released during the reaction.
Whereas the energy that must be absorbed to break the bonds in the reactants, is more than the energy that is released when the new bonds in the products are formed. This means that in the overall reaction, energy must be absorbed from the surroundings. This type of reaction is known as an endothermic reaction.

Therefore, we know that the reaction in which energy is evolved is called an exothermic reaction.

Note: We need to remember that when new bonds form, energy is released. The energy that is needed to break a bond is called the bond energy or bond dissociation energy. It is a measure of the bond strength in a chemical bond. It is the amount of energy that is needed to break the bond between two atoms.