Question

Sodium hydroxide and hydrochloric acid react as shown in this equation.
${\text{NaOH}}\left( {{\text{aq}}} \right) + {\text{HCl}}\left( {{\text{aq}}} \right) \to {\text{NaCl}}\left( {{\text{aq}}} \right) + {{\text{H}}_{\text{2}}}{\text{O}}\left( {\text{l}} \right)$
i) Which type of chemical reaction is this?
ii) The reaction is exothermic. Explains what that means.
iii) Differentiate exothermic reaction and endothermic reaction.
iv) What happens to the temperature of the solution as the chemicals react?

Answer 1

Hint: To solve this we must know that sodium hydroxide $\left( {{\text{NaOH}}} \right)$ is a base and hydrochloric acid $\left( {{\text{HCl}}} \right)$ is an acid. In the reaction, sodium chloride $\left( {{\text{NaCl}}} \right)$ is formed. Sodium chloride is also known as common salt.

Complete step-by-step answer:
i) We are given a reaction in which sodium hydroxide and hydrochloric acid react. The given reaction is as follows:
${\text{NaOH}}\left( {{\text{aq}}} \right) + {\text{HCl}}\left( {{\text{aq}}} \right) \to {\text{NaCl}}\left( {{\text{aq}}} \right) + {{\text{H}}_{\text{2}}}{\text{O}}\left( {\text{l}} \right)$
We know that sodium hydroxide $\left( {{\text{NaOH}}} \right)$ is a base and hydrochloric acid $\left( {{\text{HCl}}} \right)$ is an acid. In the reaction, sodium chloride $\left( {{\text{NaCl}}} \right)$ is formed. Sodium chloride is a salt. Along with the salt water is also produced in the reaction.
The reaction of an acid and a base to produce salt and water is known as neutralization reaction.
Thus, the type of given chemical reaction is neutralization reaction.

ii) We are given that reaction is exothermic.
The chemical reaction in which heat energy is evolved or released or given out by the substance is known as an exothermic reaction. In an exothermic reaction, the net gain in energy is negative.
Energy is released in the form of heat or light.

iii) Difference between exothermic reaction and endothermic reaction is as follows:

Exothermic reaction	Endothermic reaction
The chemical reaction in which heat energy is evolved or released or given out by the substance is known as an exothermic reaction.	The chemical reaction in which heat energy is absorbed by the substance is known as an endothermic reaction.
Energy is released from the system to the surrounding.	Energy is absorbed from the surrounding by the system.
The released energy is in the form of heat or light.	The absorbed energy is in the form of heat.
Examples: Explosions, nuclear fission, rusting of iron, etc.	Examples: Photosynthesis, melting of ice, evaporation, etc.

iv) Change in temperature as the reaction occurs is as follows:
We are given that reaction is exothermic. The chemical reaction in which heat energy is evolved or released or given out by the substance is known as an exothermic reaction. As heat is evolved during the reaction, the temperature of the solution increases. Thus, the temperature of the solution will increase as the chemicals react.

Note: Do not confuse between exothermic reaction and endothermic reaction. The chemical reaction in which heat energy is evolved or released or given out by the substance is known as an exothermic reaction while the chemical reaction in which heat energy is absorbed by the substance is known as an endothermic reaction.