1. Formation of New Substances: This is the most defining characteristic. The original substances react to form entirely new substances with different compositions and properties. For example, burning wood creates ash, carbon dioxide, and water, all of which are different from the original wood.
2. Rearrangement of Atoms: During a chemical change, atoms are rearranged and bonded differently, resulting in the creation of new molecules. This rearrangement is a fundamental process that drives the change.
3. Energy Change: Chemical changes are almost always accompanied by a change in energy, either absorbed (endothermic) or released (exothermic). This energy change can be in the form of heat, light, or sound.
4. Observable Evidence: There are often visible signs indicating a chemical change, including:
* Color change: For example, rusting iron changes from a silvery color to reddish-brown.
* Gas production: Bubbling or fizzing indicates the release of gas, like when baking soda reacts with vinegar.
* Precipitate formation: A solid forms from a solution, like when milk curdles.
* Heat or light production: A chemical reaction releases heat, like in a combustion reaction, or produces light, like in a firefly's glow.
5. Irreversibility: Most chemical changes are irreversible, meaning the original substances cannot be easily recovered by simple physical means. For example, burning a piece of paper cannot be reversed to get the original paper back.
Examples of Chemical Changes:
* Burning wood
* Rusting of iron
* Cooking an egg
* Baking a cake
* Souring of milk
* Electrolysis of water
It's important to distinguish between chemical changes and physical changes:
* Physical changes only alter the physical properties of a substance, such as shape, size, or state of matter. The chemical composition remains the same. Examples include melting ice, cutting paper, or dissolving sugar in water.
Understanding these factors helps you identify and understand the processes of chemical change.
