Chemistry – Chemical reactions - Physical and chemical changes | e-Consult

Here are three key differences between physical and chemical changes:

• Chemical Composition: In a chemical change, the chemical composition of the substance changes, resulting in the formation of new substances. In a physical change, the chemical composition remains the same.

  
  

  
  

  Example: Burning wood (chemical change - forms ash, carbon dioxide, water) vs. melting ice (physical change - remains water).

• Reversibility: Many physical changes are easily reversible (e.g., melting, freezing, boiling, condensing). Chemical changes are often difficult or impossible to reverse without further chemical reactions.

  
  

  
  

  Example: Melting ice can be reversed by cooling (physical) but burning wood cannot be easily reversed to regain the original wood (chemical).

• Energy Change: Chemical changes typically involve an energy change (either releasing energy - exothermic - or absorbing energy - endothermic). Physical changes usually involve a small energy change, or no significant energy change.

  
  

  
  

  Example: Exploding dynamite (chemical change - releases a large amount of energy) vs. boiling water (physical change - absorbs heat to change state).