Exothermic reactions range from safe, gentle to dramatic, explosive and involve interesting chemistry as well as physics reactions because the release of energy can cause sparks, flames, sounds or smokes and sometimes even sounds.
An exothermic reaction is the release of thermal energy (-ΔH) as it flows out of the system. Thermal energy is negative because energy is being released and the initial potential energy of reactants is more than the energy released from products.
Let’s explore the exothermic reactions occurring around us:
1. Cellular Respiration
This is an essential exothermic reaction that occurs in every cell and provides energy to our cells to maintain all the vital functions of our body. The sugar molecules of our body breakdowns into carbon dioxide and water molecules plus they release energy. The energy released during the breakdown of sugar is used in the synthesis of ATP which is the energy carrier molecule of the cells.
2. Ice Cubes
When water freezes into ice cubes, the energy is released in the form of heat. When water molecules begin to freeze, their particles come close and forms a new bond. As in exothermic reaction, the energy released is more when new bonds are formed than the energy required when bonds break. So, ice cube formation is an exothermic process.
3. Formation Of Snow In Clouds
The process of snow formation is an exothermic reaction. The process of condensation forms clouds and some clouds even have ice in it. So when the water molecules come close to each other and form bonds, energy is released, and this is why air feels warmer when it’s snowing.
4. Hot Packs
We all use hot packs in winters or when we are in pain; say pain in legs or headache and while treating injuries. Hot packs have two bags inside it. Inner bag contains water while outer bag have ionic salts like calcium chloride and magnesium sulfate. When these ionic salts react with water; exothermic reaction takes place and energy is released in the form of heat.
5. Rusting Of Iron
Rusting of iron is an exothermic-oxidation reaction. When the pure form of iron or alloy comes in contact with air (oxygen, Rusting occurs along with the release of heat.
6. Burning Of Candles
The burning of the candle is an exothermic reaction. The candle is a paraffin wax which is made up of hydrocarbons. When the candle burns, it comes in the contact of oxygen, and there is a breaking of hydrocarbon bonds and hence the release of energy take place. That’s why it feels warm around the burning candle.
7. Lightning Of Match
Match stick is composed of phosphorous, sulfur and other chemicals. When the matchstick is ignited, the chemical reaction takes place between the phosphorous, sulfur and air which results in fire and release of heat.
8. Setting Cement And Concrete
The chemical reaction that occurs between the cement and water is called cement hydration. Cement hydration is an exothermic process. The mixing of heat with water will result in rapid liberation of heat for a few minutes. This evolution of heat is due to the chemical substances present in the cement-like di- and tri-calcium aluminates and silicates.