What are Chemical Changes?
A chemical change is one where there are changes in the chemical properties of the components. Their chemical composition may change and the final product may have different properties as compared to the original components.
Let us take the example of an apple. When you cut it and keep it in the open for some time, you will notice that it has a brownish hue on its surface. This happens
because the acid in apple reacts with the atmospheric humidity and other trace elements present and gives the apple surface a brownish-yellow color.
Definition of Chemical Change: .
A change which alters the specific properties of a substance by bringing about a change in its molecular composition, followed by a change in its state is called chemical change.
Experiments to Show Chemical Changes:
Burning of Magnesium ribbon: When a small piece of a thin strip or ribbon of magnesium cleaned with sandpaper is brought near the flame, then it burns with a brilliant white light. On complete burning, it leaves behind powdery ash. This powdery ash is named magnesium oxide.
The above chemical change can be represented by the following chemical equation:
Magnesium ( Mg ) + Oxygen ( O2 ) ---> Magnesium oxide (2MgO)
Further, the powdery ash, Magnesium oxide is mixed in the aqueous solution resulting in the formation of a new substance. The mixture obtained is basic in nature.
Reaction of copper sulphate with iron: When copper sulphate (blue vitriol or neela thotha) is dissolved in water with a few drops of dilute sulphuric acid to the mixture. This leads to a change in the colour of the solution, i.e., the colour of the solution is blue. Further, a nail is added to the solution, which further leads to a change in the colour of the mixture from blue to green due to the formation of a new substance called iron sulphate.
Copper sulphate solution (blue) + Iron ---> Iron sulphate solution (green) + Copper (brown deposit)
Formation of carbon dioxide: When a teaspoonful of vinegar (acetic acid) is mixed with a pinch of baking soda (Sodium hydrogen carbonate), then a hissing sound is produced with the formation of gas. This obtained gas is called carbon dioxide gas. The following chemical equation represents the following chemical change:
CH3COOH(aq) + NaHCO3(aq) ---> CO2(g) + H2O(l) + CH3COONa(aq)
The gas obtained in this chemical change is further passed to lime water solution and hence the reaction between carbon dioxide and lime water yields the following chemical substance.
Carbon dioxide (CO2) + Lime water [Ca(OH)2] ---> Calcium Carbonate (CaCO3) + Water (H2O)
The new chemical substance formed here is calcium carbonate (CaCO3). This calcium carbonate makes lime water milky. Turning lime water into milky is considered as the standard test of carbon dioxide.
In the above-mentioned examples of chemical reactions, it has been seen that one or more new substances are produced in a chemical change.
Besides these newly formed substances, the following may accompany a chemical change-
Heat, light or radiation such as ultraviolet may be given off or absorbed.
Production of sound may occur
A change in smell may happen
Formation of a bubble of gas may be accompanied
Rusting of iron: Rusting of iron is considered to be a chemical change. Rust is a chemical compound that is formed when iron or any other alloy of iron is exposed to oxygen in the presence of moisture.
This is a prolonged process.
4Fe + 3O2 +2H2O ---> 2Fe2O3.H2O(Rust)
For rusting, it is essential to have both oxygen and water. If there is more humidity in the air, then the process of rusting increases. As iron is used in making bridges, ships, cars, truck bodies and in many other substances, rusting of iron leads to monetary loss as it corrodes the iron.
Preventions of Rusting:
Rusting of iron can be prevented by not allowing iron to come in contact with the moist air. Coating iron with oil, grease or paint is the simplest method to prevent the process of rusting.
Another way to prevent rusting is coating iron with another metal such as zinc or chromium. Iron pipes used in home to carry water are galvanised to prevent rusting.
As we know, there is a huge demand for iron in the ship building industry. The body of the ship is always in contact with water and the air. The salt in water speeds up the process of rusting. Use of stainless steel can help to prevent the process of rusting.
Conclusion
From the above discussion, we understood that chemical reactions happening around us are very important in our lives. Formation of new substances occurs as a result of chemical change. Digestion of food, fermentation of grapes, etc. all happen due to chemical changes. A chain of chemical reactions yields the production of several new substances. Useful materials used in our daily life such as plastics and detergents are produced as a result of chemical reactions. Indeed, new substances are produced by studying chemical changes.