Question

Give the reason for the following 
A) shiny finish appears on the wall after two-three days of white washing 
B) Generally all decomposition reaction are endothermic reactions

Answer 1

A) shiny finish appears on the wall after two-three days of white washing

• The solution used for white washing of the wall is quick lime(CaO).And when this quick lime is mixed with water it gets converted into slaked lime [Ca(OH)2]
• and on exposure to the air it finally gets converted into Calcium carbonate[CaCO3] due to which walls shine...
• 1.CaO + H2O -----> Ca(OH)2
• 2.Ca(OH)2 + CO2 -----> CaCO3

B) Generally all decomposition reaction are endothermic reactions

• Decomposition reactions are usually endothermic because they involve breaking of bonds.
• Breaking bonds requires an input of energy, while forming bonds releases energy.