Chemical Properties and Changes

Chemical Properties

• Definition: Observed during chemical reactions; involve the transformation of substances.
• Destruction of Material: In a chemical reaction, one substance is destroyed, creating a new substance.
• Examples of Chemical Properties:
  • Reactivity: How a substance interacts with other substances (e.g., oxygen).
  • Stability: Ability of a substance to remain unchanged under set conditions.
  • Flammability: Important for safety, especially in firefighting; involves combustion reactions producing heat and flames.
  • Heats or Enthalpies of Reaction: Characteristic energy changes occurring during reactions, often found in reference manuals.
  • Oxidation-Reduction Potentials: Measured during redox reactions; important in various chemical processes.

Biological Activity and Toxicity

• Importance in Healthcare: Relates to how chemicals interact in biological systems (e.g., toxicity when ingested).
• Ingestion: In the stomach, chemicals undergo transformations—this destructive process relates to chemical properties.

Physical vs. Chemical Changes

• Physical Change: Substance maintains identity and composition (e.g., boiling water - water vapor remains water).
• Chemical Change: Substance is destroyed, and a new substance is formed (e.g., rusting of iron, digestion of food).
• Distinguishing: Evaluate whether there is destruction to the original substance.

Pure Substances

• Definition: A material with a definite and fixed composition that can be measured (e.g., specific melting/boiling points).
• Impurity Indicators: A range of melting points suggests a substance is impure.

Homogeneous vs. Heterogeneous Mixtures

• Homogeneous Mixture: Uniform composition throughout; samples from different areas yield same composition. In other words, a homogeneous mixture is also called a solution.
• Heterogeneous Mixture: Contains two or more distinct phases; different samples exhibit varying compositions.
• Phases: Homogeneous parts of a system. For example, ice water has two phases (solid and liquid), but the composition is uniform (both water).

Matter and Energy

• Matter Definition: Anything that has mass and occupies space. Energy differs as it does not have mass (e.g., sunlight).

Mixtures and Separation Techniques

• Definition: Mixtures consist of two or more pure substances.
• Separation Techniques: Typically based on physical properties (e.g., magnetism for iron in sand).
• Historical Context: Early chemists sought to isolate pure substances from mixtures and used physical properties for separation.

Elements and Compounds

• Elements: Substances that cannot be chemically broken down (comprised of a specific type of atom).
• Compounds: Composed of two or more elements combined in fixed proportions, capable of being broken down through chemical means.