Question

Classify chemical reactions on the basis of energy change that takes place during a reaction.

Answer 1

• Certain reactions are accompanied by the liberation or absorption of heat energy.
• On the basis of energy change reactions are categorized into exothermic and endothermic reactions.

Exothermic reaction- The type of reaction in which heat energy is released to get products from the reaction of reactants is known as an exothermic reaction.

• Example- Burning of magnesium ribbon in the air to give Magnesium oxide, heat, and light is an example of the exothermic reaction.
• $\underset{\mathrm{Magnesium}}{2\mathrm{Mg}\left(\mathrm{s}\right)}+\underset{\mathrm{Oxygen}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}\stackrel{\mathrm{Burning}}{\to }\underset{\mathrm{Magnesium}\mathrm{oxide}}{2\mathrm{MgO}\left(\mathrm{s}\right)}$

Endothermic reaction- Endothermic reactions are chemical reactions in which the reactants absorb heat energy from the surroundings to form products.

• Example- When sodium bicarbonate is heated strongly, it converts into sodium carbonate, steam and carbon dioxide gas.
• $\underset{\mathrm{Sodium}\mathrm{bicarbonate}}{{\mathrm{NaHCO}}_3\left(\mathrm{s}\right)}\stackrel{∆}{\to }\underset{\mathrm{Sodium}\mathrm{carbonate}}{{\mathrm{Na}}_2{\mathrm{CO}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Steam}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)}$