Reversible and Ireversible changes

Reversible changes are temporary

Examples of reversible changes:

  • Evaporating : eg water from a puddle evaporating on warm day
  • Dissolving eg sugar dissolving in hot tea
  • Melting eg chocolate melting when it gets warm
  • Freezing eg water freezing when it cools down below 0C
  • Boiling eg water boiling when it is heated to 100C
  • Condensing eg steam condensing on a cold bathroom mirror

d) about reversible changes, including dissolving, melting, boiling, condensing, freezing and evaporating
e) the part played by evaporation and condensation in the water cycle

All the changes above are temporary can be easily reversed.

They are sometimes called physical changes and no new chemicals are formed.

Several of the changes above take place in the Water Cycle

Ireversible changes are Permanent

 Examples of ireversible changes:

  • Making toast
  • Cooking an egg
  • Rusting
  • Burning (eg burning wood)
  • Reacting baking soda with vinegar

The changes above are permanent and cannot be reversed .

They are sometimes called chemical changes and always result in a new chemical substance being formed.

When a new substance is formed it means that a chemical reaction has taken place.

Signs that a chemical change is taking place:

      1. A change in temperature (it will usually get hot)
      2. A colour change (eg a blue chemical turns white)





Burning is an example of an ireversible change


The Fire Triangle

To produce any fire three things are always needed

FUEL: something to burn

OXYGEN: this comes from the air. More air = more oxygen.

HEAT: Nothing will burn if the temperature is not high enough

When something burns a new chemical is always produced