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# Chemical Reactions and Elements **Identifying Chemical Reactions**: Chemical reactions involve the transformation of reactants (starting materials) into new products with different properties. - **Matter changes**: Reactants change to form products with different properties. - **Energy change...

# Chemical Reactions and Elements **Identifying Chemical Reactions**: Chemical reactions involve the transformation of reactants (starting materials) into new products with different properties. - **Matter changes**: Reactants change to form products with different properties. - **Energy change**: Energy is either absorbed or released during a chemical reaction. **Example**: - Magnesium reacting with oxygen to produce magnesium oxide. **Physical vs. Chemical Reactions**: - **Physical reactions**: Change state or form (e.g., melting ice). - **Chemical reactions**: Produce new substances with different properties. **Hoffmann Apparatus (for water electrolysis)** * Diagram of the apparatus: A U-shaped tube with two electrodes connected to a power source. The tube is filled with water. * **Electrolysis of water:** Water is decomposed into hydrogen and oxygen gases by passing an electric current through it. * **Gases produced**: Hydrogen gas is produced at one electrode, and oxygen gas is produced at the other. * **Hydrogen**: Gas collected at one electrode. * **Oxygen** Gas collected at the other electrode. **Elements and Compounds**: - **Reinstoffe (Pure Substances)**: Can be elements or compounds. - **Elements**: Cannot be broken down into simpler substances by chemical means. - **Compounds**: Combinations of two or more elements chemically bonded together. **Dalton's Atomic Model**: 1. **Atoms are indivisible and indestructible**: Building blocks of matter. 2. **Atoms of the same element have identical properties**: Same mass, size etc. 3. **Different elements have different properties**: Different masses and sizes. 4. **Compounds**: Composed of atoms of two or more elements combined in specific ratios. 5. **Chemical reactions**: Involve the rearrangement of atoms. **Molecules**: - **Formation**: Atoms join together through chemical bonds to form molecules. **Examples of Elements and Compounds**: - **Elements**: Hydrogen, Nitrogen, Carbon, Oxygen, Sulphur, etc. - **Compounds**: Water (H₂O), Carbon dioxide (CO₂), Ammonia (NH₃), etc. **Models**: * Diagrams of molecules (like H2O, CO2) using different colored circles to represent different atoms. **Additional Notes (from the image):** - Descriptions of different chemical concepts - Symbols and diagrams showing molecular representations.