What are physical and chemical changes

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What are physical and chemical changes?
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• How can you distinguish between physical and
  chemical changes in matter ?
• What evidence can I look for to determine the
  type of change ?

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Key Terms

• Physical change
• Chemical change
• Reactivity
• Oxidation
• Precipitate

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Physical and Chemical Changes

• The changes matter undergoes are classified as
  either physical changes or chemical changes.
• Do changes occur in fireworks?

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Physical Change

• A process in which a substance changes its
  physical form or appearance but not its basic
  composition is called a physical change.
• Molecules of a substance are rearranged, not
  changed into a new substance.

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Some examples of physical changes are

• cutting a piece of paper
• ice melting
• boiling water
• drawing copper into a fine wire
• separating out water from seawater
• separating out oxygen gas from air
• Do fireworks undergo a physical change ?

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Chemical Change

• Chemical changes are always changes in the
  composition and form of a substance.
• In a chemical change, matter is transformed
  completely into different materials with new
  properties.
• The type of chemical change that a substance can
  undergo is determined by its chemical properties.
  
• Molecules are changed into new matter!

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Some examples of chemical changes are

• iron turning into rust in moist air
• extracting sulfur from car battery acid
• overtime, a battery loses its charge
• digesting food into sugar to use with cells

Do fireworks undergo chemical changes ?
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Evidence of Change in Fireworks?
Burning of fuel and oxidizers produce
oxygen Explosion - reducing agents use oxygen to
produce hot gases that control speed
Production of light in various colors based on
chemicals reacting to heat Production of new
substances What type of change occurred
here?
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Fireworks Chemical Properties
Flammable - can burn Chemicals react to cause
explosion Produces heat, light and gases
What type of change do fireworks undergo ?
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Signs of Physical Change

• Changes do not create new matter
• - color change
• - shape change
• - size change
• - state change ( ie boiling water)
• - molecules are rearranged but not changed

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Signs of Chemical Change

• Changes do create new matter
• production of energy in form of heat and/or light
• (increase or decrease temperature)
• formation of precipitate - settles out of
  solutions
• color change
• - production of gas - bubbles evident
• - new matter properties are present

Molecules of matter are changed into new
substances with different properties !
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Chemical Changes Occur in Fireworks

• New matter created
• Gases are produced
• Heat released and light is produced
• No evidence of original matter remains
• Color change produced

No one sign determines what type of change occurs
- always look for multiple signs