Question

Which reaction is exothermic?

Answer 1

Hint:Chemical reactions are those reactions in which reactants get converted into products under some conditions like at fixed temperature and pressure and some reactions proceed with the help of catalysts which increase their rate of reaction.

Complete step-by-step answer: Chemical reactions when proceed then some amount of energy is released or in some reactions some energy is absorbed on this basis the reactions are divided into two categories called as exothermic reactions and endothermic reactions.
An exothermic reaction can be defined as a chemical reaction in which energy is released in the form of heat or light whereas in endothermic reactions heat is absorbed by the system. In case of exothermic reaction energy is transferred into the surroundings rather than taking energy from surroundings. An exothermic reaction can be shown as:
$A\to B+Energy$; Where A is reactant and B is product and energy is released during the reaction. It is the reaction in which change in enthalpy will be negative and overall change in Gibbs free energy is also negative. A strongly exothermic reaction will usually be exergonic in nature because $\mathrm{\Delta }H{}^{\circ }$ makes a more contribution to $\mathrm{\Delta }G{}^{\circ }$. The main examples of exothermic reaction are combustion, thermite reaction, polymerization etc.

Note: If we see the daily life examples then hand warmers make use of the oxidation of iron to achieve an exothermic reaction. Rather than this some uncontrolled exothermic reactions lead to fires and explosions which will be very dangerous for us.