Physical and Chemical Changes

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Physical and Chemical Changes
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Substances

• What is a substance?
• Matter that has a definite composition aka a
  chemical
• Examples
• Table salt, pure water
• Non-examples
• Sea water, tap water (their compositions can vary
  from one place/time to another)

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States of Matter

• Solids definite shape and volume
• Particles are tightly packed
• Examples wood, wax, concrete
• Liquids definite volume, takes the shape of its
  container
• Particles are less tightly packed than a solid
• Examples water, blood, mercury
• Volume can expand when heated

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States of Matter- continued

• Gases no definite volume, no definite shape
  (expands to fill the container)
• Compared to solids liquids the molecules are
  FAR apart
• Examples helium, neon, oxygen
• Do the terms vapor and gas mean the same thing?
• No! The term gas refers to a substance that is in
  the gaseous state at room temp and vapor refers
  to a gaseous substance that is in the liquid or
  solid state at room temp.

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Physical Properties of Matter

• A physical property can be observed or measured
  without changing the samples composition.
• Extensive Properties depend on the amount of a
  substance present (length volume)
• Intensive properties independent of how much
  material is present (density, color)

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Physical Properties

• Examples
• - Melting Point of water is 0o C
• Copper is a reddish brown color
• Pine (wood) is less dense than water

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Chemical Properties of Matter

• Definition
• Ability of a substance to combine with or change
  into one or more other substances
• Examples
• - copper forms a new compound when
  exposed to air (that green color)
• - iron forms rust when exposed to air

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Changes in Matter Physical vs. Chemical

• Physical Change You still have the same
  chemical substance that you started with
• When ice melts it is a physical change, you still
  have water, its just in a different state (phase
  change)
• When I rip a piece of paper, its still paper
• Chemical Change One or more substances change
  into a new substance
• When I burn a piece of paper I no longer have
  paper
• Rust forming is a chemical change

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Evidence that a chemical reaction has taken place

• Color Change
• Energy Change (gets warmer or colder)
• Precipitate forms (new solid)
• Gas is produced (bubbles are given off)

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Law of Conservation of Mass

• Mass is neither created nor destroyed during a
  chemical reaction it is conserved
• Mass reactants Mass products

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Mixtures of Matter

• What is a mixture?
• Combination of 2 or more substances where each
  substance retains its original property
• Examples coins in a piggy bank, salad, mixture
  of sand salt

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Types of Mixtures

• Heterogeneous mixture is NOT the same
  throughout
• Examples Italian salad dressing, orange juice
  containing pulp

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Types of Mixtures continued

• Homogeneous Mixture that has a constant
  composition throughout (always just one phase)
• Examples mercury amalgam (silver fillings in
  your teeth), Kool-aid,
• Can also be called a solution
• Can be solids, liquids, or gases or a combination
  of these
• Alloy a solid-solid solution (made to achieve
  greater strength and durability)
• Examples brass (copper and zinc) and steel
  (iron and carbon)

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Methods used to separate mixtures

• Filtration uses a porous barrier to separate a
  solid from a liquid (think of a coffee filter)
• Distillation based on differences in boiling
  points (think making moonshine)
• Crystallization a solid is formed from a liquid
  solution (think rock candy)
• Sublimation Solid changes to a vapor without
  going through the liquid stage (think dry ice)
• Chromatography separates parts of a mixture
  based on ability to travel at certain rates
  (think how some substances are picked up more
  slowly than others with a paper towel)

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Elements

• Element pure substance made up of 1 kind of
  atom and cannot be separated into simpler
  substances (think gold, silver, oxygen)
• 92 elements occur naturally on Earth, the rest
  are man-made

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Compounds

• Two or more substances (usually elements) that
  are CHEMICALLY combined.
• NaCl, H2O, (notice these each contain 2
  elements)
• Properties of compounds are DIFFERENT from the
  elements that make them up.