Question

What are exothermic and endothermic reactions? Explain with suitable

examples​

Answer 1

Answer:

Many chemical reactions release energy in the form of heat, light, or sound. These are exothermic reactions. Exothermic reactions may occur spontaneously and result in higher randomness or entropy (ΔS > 0) of the system. They are denoted by a negative heat flow (heat is lost to the surroundings) and decrease in enthalpy (ΔH < 0). In the lab, exothermic reactions produce heat or may even be explosive.

There are other chemical reactions that must absorb energy in order to proceed. These are endothermic reactions. Endothermic reactions cannot occur spontaneously. Work must be done in order to get these reactions to occur. When endothermic reactions absorb energy, a temperature drop is measured during the reaction. Endothermic reactions are characterized by positive heat flow (into the reaction) and an increase in enthalpy (+ΔH).

Examples of Endothermic and Exothermic Processes

Photosynthesis is an example of an endothermic chemical reaction. In this process, plants use the energy from the sun to convert carbon dioxide and water into glucose and oxygen. This reaction requires 15MJ of energy (sunlight) for every kilogram of glucose that is produced:

sunlight + 6CO2(g) + H2O(l) = C6H12O6(aq) + 6O2(g)

Other examples of endothermic processes include:

Dissolving ammonium chloride in water

Cracking alkanes

Nucleosynthesis of elements heavier than nickel in stars

Evaporating liquid water

Melting ice

An example of an exothermic reaction is the mixture of sodium and chlorine to yield table salt. This reaction produces 411 kJ of energy for each mole of salt that is produced:

Na(s) + 0.5Cl2(s) = NaCl(s)

Other examples of exothermic processes include:

The thermite reaction

A neutralization reaction (e.g., mixing an acid and a base to form a salt and water)

Most polymerization reactions

Combustion of a fuel

Respiration

Nuclear fission

Corrosion of metal (an oxidation reaction)

Dissolving an acid in water

Answer 2

Exothermic reaction :

• When energy is released in the form of heat during the reaction, it is called an exothermic reaction. The heat evolved is shown by a plus sign on the right-hand side of the equation.

For example :

$\sf N_{2} (g) + 3 H_{2} (g) \longrightarrow 2NH_{3} (g) + 92 kJ$

Endothermic reaction :

• When energy is absorbed as heat during a reaction it is called an endothermic reaction the heat absorbed is shown by a plus sign on the left hand side of the equation or with the negative side on right hand side.

For example :

$\sf N_{2} (g) + O_{2} (g) + 180 kJ \longrightarrow 2NO (g)$

⠀ ⠀⠀ ⠀ ⠀⠀ OR

$\sf N_{2} (g) + O_{2} (g) \longrightarrow 2NO (g) - 180 kJ$