Chemical reactions and reversible changes | Year 5 Science PDF Download

Overview of Chemical Reactions

• A chemical reaction leads to the formation of new materials, often resulting in irreversible changes.
• In a chemical reaction, new substances are always created, and sometimes these new substances are beneficial to us.

Examples of Irreversible Changes

• Heating: Heating substances can bring about irreversible changes. For instance, when a raw egg is heated to cook it, the cooked egg cannot revert to its raw state.
• Mixing: Combining substances can result in an irreversible change. For example, when vinegar and bicarbonate of soda are mixed, the resulting reaction produces carbon dioxide bubbles. The resultant mixture of bubbles and liquid cannot be transformed back into vinegar and bicarbonate of soda.
• Burning: Burning exemplifies an irreversible change. When wood is burned, it produces ash and smoke. The ash and smoke cannot be converted back into wood.

Examples of reversible changes

• A reversible change refers to a change that can be undone or reversed. Examples of reversible changes include:
  • Dissolving: Sugar dissolving in water.
  • Melting: Ice melting into water.
  • Freezing: Water freezing into ice.
  • Evaporation: Water evaporating into vapor.
  • Mixing: Mixing salt in water
• If you can retrieve the original substances after a reaction, it signifies a reversible reaction. For instance, water can be frozen to form ice, but upon heating, the ice melts back into water.
• A reversible change may alter the appearance or texture of a material and sometimes results in the formation of new substances.