2. Energy is either absorbed or released: Chemical changes often involve the absorption or release of energy. This can be seen in the form of heat, light, or electricity. For example, when wood burns, it releases heat and light energy.
3. Irreversible changes: Chemical changes are generally irreversible. This means that the original substances cannot be reformed from the products of the reaction. For example, once sugar is burned, it cannot be turned back into sugar.
4. Formation of gas: Chemical changes may result in the production of gas. This can be observed by the formation of bubbles or a change in volume. For example, when baking soda reacts with vinegar, carbon dioxide gas is produced, causing bubbles to form.
5. Change in chemical composition: Chemical changes always involve a change in the chemical composition of the reactants. This means that the elements present in the original substances are rearranged to form new compounds. For example, when water molecules are broken down by electrolysis, the elements hydrogen and oxygen are produced.
6. Change in pH: Chemical changes may cause a change in the pH of a solution. This can be observed by using a pH meter or indicator. For example, when an acid is added to a base, the pH of the solution decreases.
7. Precipitation: Chemical changes may result in the formation of a precipitate. This is a solid that forms when two solutions are mixed and the dissolved substances react to form an insoluble compound. For example, when silver nitrate is added to sodium chloride solution, a white precipitate of silver chloride forms.
