Physical and Chemical Changes

• In Chemistry, matter can go through physical and chemical changes.
• In this document, you will find the information necessary in order to form the foundation of the knowledge of physical and chemical changes.

Chemical Changes

• A chemical change involves the formation of new products, such as when a chemical reaction occurs.
• Chemical changes involve the rearrangement of atoms, which means chemical bonds are broken or formed.
• These changes are sometimes difficult to reverse and adhere to the laws of conservation (meaning atoms cannot be created nor destroyed).

Example: Electrolysis of Water

• A chemical change is conducted with the electrolysis of water (when electricity passes through water).
• In this reaction, the bonds that form break and reform as and .
• This forms three covalent bonded diatomic molecules. See Bonding.

Indicators

• A chemical change can be associated and observed through the following signs.
  • Change in temperature
  • Change in colour
  • Change in odour
  • Formation of a solid precipitate
  • Formation of bubbles
• This is all caused by the breakage and formation of bonds, and the formation of new substances.
• Referring back to the electrolysis example, you can observe the formation of bubbles in the water from the electrodes due to the hydrogen and oxygen gas produced.

Physical Changes

• A physical change does not involve the formation of new products, but rather it will undergo a change in state or shape or the mixing with something else. An example of this would be a change in its state of matter, such as the freezing of water to ice.
  • In the physical change of freezing water to ice, the molecules are not affected but the water’s state of matter has changed from liquid to solid (and its volume has expanded).
• Unlike a chemical change, a physical change is easily reversible.