1. Composition: This is the most fundamental change. New substances are formed with different chemical compositions than the original reactants. For example, when you burn wood, you're changing the composition of wood (cellulose, lignin) into carbon dioxide, water vapor, and ash.
2. Chemical Properties: These are properties that describe how a substance reacts with other substances. For example, the ability of a substance to burn (flammability) or to react with an acid are chemical properties. These properties change because the substances involved in the reaction are now different.
3. Physical Properties: These properties can be observed without changing the chemical composition of a substance. Examples include:
* Color: Many chemical reactions result in a change of color. Think of rust forming on iron.
* Odor: The smell of burning wood is different from the smell of wood itself.
* Density: Mixing two liquids can create a solution with a different density than either starting liquid.
* Melting point and boiling point: These can change due to the formation of new substances.
* Solubility: The ability of a substance to dissolve in a solvent can change after a chemical reaction.
Important Note: It's crucial to remember that *energy is always involved* in a chemical reaction. It can be released (exothermic reaction) or absorbed (endothermic reaction). This energy change is also a property that changes during a chemical reaction.
In summary, a chemical reaction fundamentally alters the composition of matter, leading to changes in chemical, physical, and energetic properties.
