Observe the following changes and classify them as exothermic and endothermic changes

List :- Burning of charcoal, decomposition of  ${\text{CaCO}}_3$. Respiration, photosynthesis, evaporation, Burning of crackers

Exothermic reactions:

i) During respiration oxidation of glucose takes place which produces large

amount of heat energy.

${\text{C}}_{\text{6}}{\text{H}}_{\text{12}}{\text{O}}_{\text{6}}+6{\text{O}}_{\text{2}}\to 6{\text{CO}}_{\text{2}}+6{\text{H}}_{\text{2}}\text{O}+\text{Energy}$

So, it is an exothermic reaction.

ii) Bursting of crackers produces large amount of heat and light

iii) Burning of charcoal produces ${\text{CO}}_{\text{2}}$  heat and light.  So, all the reactions are considered as exothermic.

Endothermic reactions:  $C_{\left(s\right)}+O_{2\left(g\right)}\to C{O}_{2\left(g\right)}+Heat$ 

i) Decomposition of  ${\text{CaCO}}_3$ takes place with the help of heat.

${\text{CaCO}}_{\text{3}}\stackrel{\Delta }{\to }\text{CaO}+{\text{CO}}_{\text{2}}$

ii) During photosynthesis plants use the energy from the sun to convert  ${\text{CO}}_{\text{2}}\&{\text{H}}_{\text{2}}\text{O}$  into glucose and oxygen.

$6C{O}_2+6H_{2}O\underset{light}{\overset{sun}{\to }}{C}_6{H}_{12}{O}_6+6O_{2\left(g\right)}$

iii) During evaporation the liquid  ${\text{H}}_{\text{2}}\text{O}$ converts into water vapour at any temperature below its boiling point.

$H_2{O}_{\left(l\right)}\stackrel{\Delta }{\to }{H}_2{O}_{\left(g\right)}$

So, all the above reactions are endothermic.