Question 21.
Identify the endothermic and exothermic reaction.
a. HCl + NaOH → NaCl + H2O + heat
b. 2KClO3(s) 
2KCl(s) + 3O2↑
c. CaO + H2O → Ca(OH)2 + heat
d. CaCO3(s) CaO(s) + CO2 ↑
Answer:
Exothermic reaction: A reaction in which heat is released when reactants changes into products.
Endothermic reaction: A reaction in which heat is either supplied or absorbed from the surroundings.
a. HCl + NaOH → NaCl + H2O + heat
The given reaction is exothermic because in the reaction heat is released when reactants transformed into products.
b. 2KClO3 (s) 2KCl(s) + 3O2↑
The given reaction is an endothermic reaction because in the reaction, heat has been supplied to continue the process.
c. CaO + H2O → Ca(OH)2 + heat
The given reaction is an exothermic reaction because in the reaction heat is released when reactants transformed into products.
d. CaCO3 (s) CaO(s) + CO2↑
The given reaction is an endothermic reaction because in the reaction, heat has been supplied to continue the process.
