* Pure substances: These are substances that have a fixed and definite composition, meaning they are made up of only one type of atom or molecule. Examples include:
* Elements: Iron (Fe), Gold (Au), Oxygen (O2)
* Compounds: Water (H2O), Salt (NaCl), Sugar (C12H22O11)
* Chemical reaction: When two or more pure substances interact to form new substances with different properties, a chemical reaction has occurred. The atoms in the original substances rearrange and form new bonds.
Examples of Chemical Reactions:
* Burning: When you burn wood, the wood (a complex mixture of substances) reacts with oxygen from the air, producing ash, carbon dioxide, and water.
* Rusting: When iron reacts with oxygen and water, it forms iron oxide (rust), a new substance with different properties.
* Baking: When you mix flour, eggs, sugar, and baking soda, a complex chemical reaction occurs, producing a cake with a different texture and taste than its ingredients.
Important Points:
* Chemical reactions involve the breaking and formation of chemical bonds.
* The products of a chemical reaction have different chemical and physical properties than the reactants.
* The chemical reaction might require energy (endothermic) or release energy (exothermic).
Let me know if you have more questions about specific types of chemical reactions or examples!
