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8 September 2008

8 September 2008. Chapter 3 Notes. Mr. Herbst Room 2705. Chapter 3: Matter – Properties and Changes. 3.1 Properties of Matter Substances Pure substances have uniform and unchanging compositions Pure water = H 2 O (yes) Seawater = H 2 O + NaCl + NaBr + … (no).

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8 September 2008

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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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