Chemical Change vs. Physical Change

Key Differences

• Chemical Reaction: Changes the composition of substances
• Physical Change: Alters appearance, smell, or display but not composition

Physical Changes

• Changes in appearance or state without changing the composition
• Common changes include:
  • Texture: E.g., sanding wood changes texture without altering composition
  • Color: Painting a car changes color but not composition
  • Temperature: Heating a pan is a physical change, not altering its chemical makeup
  • Shape: Folding money changes shape, not composition
  • Change of State: E.g., ice melting to water (endothermic), water freezing (exothermic)

Physical Properties

• Luster: Interaction with light, common in metals
• Malleability: Ability to deform under stress (metals)
• Ability to be drawn into a thin wire (Ductility)
• Density: Mass per unit volume, affects buoyancy
• Viscosity: Resistance to deformation, varies with substance thickness

Chemical Changes

• Occur when the substance's composition changes due to bond formation or breaking
• Indicators include:
  • Change in Temperature: Often indicates a reaction
  • Change in Color: E.g., rusting of metal
  • Noticeable Odor: E.g., smell of rotten egg due to decomposition
  • Formation of Precipitate: Solid forming in a solution
  • Formation of Bubbles: Gas formation, often with temperature change

Exercises

1. Chemical Reaction: Dropping a sliced orange into sodium hydroxide
2. Physical Reaction: Shattering glass with a baseball
3. Chemical Reaction: Bicycle rusting
4. Physical Reaction: MacBook falling out of a window
5. Chemical vs Physical:
   • Burning leaves (Chemical)
   • Cutting diamonds (Physical)
   • Crushing a pencil (Physical)
   • Enzyme breaking down food (Chemical)
   • Salt mixing in water (Neither definitive chemical nor physical change)

References

• Books:
  • "General Chemistry: the Essential Concepts" by Raymond Chang
  • "Chemistry for Dummies"
  • "General Chemistry Principles and Modern Applications" by Ralph H. Petrucci

Additional Information

• For more on properties of matter and chemical reactions, see provided links in the reference section.