Question

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Some solution processes are endothermic and others are exothermic. Provide a detailed molecular interpretation for the difference.

Answer 1

Endothermic Process

A Process in which a Chemical reaction absorbs energy from the environment is an Endothermic Process. Here the absorption of energy is used for the sustainability of the reaction.

Ex. Ice cubes absorbs heat energy from the environment, it gets melted.

Exothermic Process

In contrast, Exothermic Process in which the energy is released to the Surroundings in the chemical reaction. Not only the heat energy, light energy, sound energy and electrical energy may also be released in the Exothermic Process. In this process energy gets released from the reaction.

Ex. When Calcium Chloride reacts with water the heat energy is released in the reaction.

Some solution process are endothermic and others are exothermic

In dissolution Process there will be a separation of solute molecules and they are bounded by solvent molecules. During this action the energies combined with this processes are

a) For the Solute molecules to get scattered, some amount of energy is needed.

b) When the solvent molecules approach the solute molecules , some energy is released.

Some extra energy is released as heat(exothermic), when the energy needed for separating the solute molecules is less than the energy released during the interaction of the solvent and the solute.

In vice versa when the energy needed for separating the solute molecules is more than the energy released during the association of solvent-solute interaction there in an energy deficit.

Both extra energy and some deficit energy are absorbed from the surrounding.

The consequence of the chemical results are by the breakage and by the formation of the bonds between the atoms and the molecules. There is a possibility of both breakage of bonds and formation of the bonds in the reaction. The bonds which present already while breaking they need energy. The energy get released during the formation of bonds .

The nature of the molecules and atoms are responsible for the energy needed to break the bonds.

Molecular interpretation for the difference

For Endothermic Reaction

Chemical Reaction between Ammonium Nitrate(NH₄NO₃) and water(H₂O) to form Ammonium hydroxide(NH₄OH) and Nitric acid (HNO₃). It absorbs heat from the surrounding and produce a cooling effect.

The reaction will be

NH₄NO₃ + H₂O -------> NH₄OH +  HNO₃

Ammonium nitrate which contains a tight package of ionic bonds, when reacts with water the association between these ions and polar water molecules leads to the dispersion of ions by polar water molecules. The reaction among the ammonium nitrate and the water molecules will produce some heat energy(exothermic reaction). This will be a very little amount compared to the energy required for the dispersion of strong ionic bonds of the ammonium nitrate. But the total process is Endothermic in which the energy gets absorbed from the surrounding.

For Exothermic Reaction

Combustion reaction of Methane

The reaction can be

CH₄ + O₂ ------> CO₂ + H₂O + Heat

Usually exothermic oxidation reactions are combustion reactions whereas it produces heat. Here Carbondi oxide and water are combustion products which is produced by the reaction of Hydrocarbons and oxygen. Breakage of bonds between Hydrocarbons and Oxygen are restored by Carbon di oxide and water bonds. The energy released for the formation of the Carbondi oxide and water is more than the energy needed for the breakage of the bonds between Hydrocarbons and oxygen bonds. As a result energy is produced in a long range.