Desirable and Undesirable Changes in Chemistry

Desirable and Undesirable Changes

• Desirable changes are useful and beneficial, such as ripening of fruit, growth in living beings, and changes involved in cooking
• Undesirable changes are harmful and cause damage, such as rusting of iron, spoiling of food, earthquakes, cyclones, and volcanic eruptions

Physical and Chemical Changes

• Physical and chemical changes are classified by chemists
• Physical changes are reversible and do not form new substances

Physical Changes

• Definition: a change in which no new substances are formed and can be reversed by reversing the conditions
• Examples of physical changes include:
  • Changes in the state of matter
  • The glowing of a heater or a bulb (reversible and no new substances formed)
  • The melting of a solid (e.g. ice, butter, sulphur, iron, lead, silver, gold) (reversible and no new substances formed)
  • The freezing of a liquid (e.g. water) (reversible and no new substances formed)
  • Sublimation (some solids directly form vapors without melting, and when cooled, vapors are directly converted into the solid) (reversible and no new substances formed)

This quiz covers the classification of changes into physical and chemical changes, and the differences between desirable and undesirable changes.