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Understanding Matter: Properties, Changes, and Mixtures

This chapter provides an in-depth exploration of the properties and changes of matter. It categorizes matter into pure substances, mixtures, elements, and compounds, highlighting the differences and characteristics of each. Key distinctions are made between physical and chemical properties, including extensive and intensive properties. It also discusses states of matter (solids, liquids, gases, and plasma) and details physical and chemical changes. The Conservation of Mass is emphasized, alongside the Law of Definite Proportions, essential for comprehending chemical reactions.

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Understanding Matter: Properties, Changes, and Mixtures

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  1. 8 September 2008 Chapter 3 Notes Mr. Herbst Room 2705

  2. Chapter 3: Matter – Properties and Changes 3.1 Properties of Matter • Substances • Pure substances have uniform and unchanging compositions • Pure water = H2O (yes) • Seawater = H2O + NaCl + NaBr + … (no)

  3. Physical Properties - Characteristics that can be observed or measured without changing the substance’s composition. • Density, color, odor, taste, hardness, melting point (mp), boiling point (bp) • Extensive Properties • Depend on how much material is there • Mass, length, volume, color. • Intensive Properties • Independent of amount of substance • Density, mp, bp, etc.

  4. Chemical Properties - Ability of a substance to combine with or change into other substances • Iron can rust (yes). Gold does not rust (yes). • Paper tears (no). Paper can burn (yes).

  5. States of Matter • Solids: definite shape & volume: incompressible: atoms stay in place • Liquids: definite volume, changes shape to match container: atoms & molecules slide past each other: almost incompressible • Gases: indefinite shape & volume: expands to fill container: particles in rapid, constant motion, highly compressible. • Plasma, high temperature.

  6. 3.2 Changes in Matter • Physical Changes • Cutting, bending, tearing, etc. • Changes of state

  7. Chemical Changes - Make new substances • iron + water + oxygen -> rust • Explode, oxidize, burn, etc. • 5 things that indicate CC: • Production of a gas (bubbles). • Production of a precipitate (ppt) (solid) • Change in Odor • Change in color • Change in energy (give off heat and/or light)

  8. Conservation of Mass • Mass is not created or destroyed in a chemical reaction • Mass reactants = Mass products. • Antoine Lavoisier (1743-1794) early chemist, studied HgO -> 2Hg+O2

  9. 3.3 Mixtures of Matter • Mixtures - Combinations of pure substances • Heterogeneous Mixture – distinct areas of different substances – Italian salad dressing • Homogeneous Mixture • Constant composition & single phase – Sugar cookie dough • Also called solutions. Solid solutions also called alloys.

  10. 3.4Elements and Compounds • Elements - Pure substance that can’t be separated into simpler substances by chemical or physical means. • 94 naturally occurring elements • H – 75% mass of universe • O + Si – 75% mass of earth’s crust • O, H, C > 90% of you

  11. Compound- 2 or more elements combined chemically: Na + Cl2 NaCl • ~ 10 x 106 known compounds • examples: NaCl H2O • Can be broken down chemically into simpler substances • H2O electrolysis>H2 + O2

  12. Law of Definite Proportions (Law of Constant Composition) • Elements in a compound always have the same mass proportions. • Percent by mass = (mass of element / mass of compound) X 100.(exactly)

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