Correct Option
The correct option isIt is a neutralization reaction which is exothermic in nature.
Explanation
The reaction between an acid and a base to form salt and water is known as a neutralization reaction. These reactions are chemical changes and are generally accompanied by the evolution of heat.
Detailed Analysis
- Reactants: Lime water contains calcium hydroxide [Ca(OH)2], which is a base. Dilute sulphuric acid [H2SO4] is a strong acid.
- The Reaction: When mixed, they undergo a neutralization reaction:
Ca(OH)2 (aq) + H2SO4 (aq) → CaSO4 (s) + 2H2O (l) - Exothermic Nature: Neutralization involves the combination of hydrogen ions (H+) from the acid and hydroxide ions (OH−) from the base to form water molecules. This bond formation process releases a significant amount of energy in the form of heat. Consequently, the temperature of the reaction mixture rises.
- Analysis of Incorrect Options:
- It is a physical change involving the release of latent heat.: This is incorrect because the reaction involves the formation of new substances (salt and water), making it a chemical change, not a physical one.
- Lime water naturally releases heat when agitated.: Agitation alone does not generate significant heat; the heat is a result of chemical bond formation.
- Sulphuric acid absorbs heat from the surrounding air.: The acid does not absorb heat from the surroundings; rather, the system releases heat generated by the internal chemical potential energy change.
Key Takeaway
Neutralization reactions are always exothermic because the formation of O-H bonds in water molecules releases energy, causing the reaction mixture to become hot.