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Subject knowledge: Changes of state

Often children can be confused around the vocabulary of changes of state and mix up concepts with each other. How often have children told you that sugar has melted in the tea?

It is key that the children have a firm understanding of the terms and choose the correct one to define what they are observing.

Each change of state (at primary level) is associated with either cooling or heating a material. There are changes of state that are associated with applying pressure (further explanation from BBC Bitesize).

Melting : This is the process by which a solid changes into a liquid usually through the application of heat. Melting occurs when the internal energy of the solid increases, (vibrates) to the point where the molecules become less ordered. As you heat up a solid the particles vibrate more as they gain more energy, until the solid reaches melting point.

Freezing: This is the process by which a liquid becomes a solid, usually through the loss of heat energy. The energy of the particles has been transferred to the surroundings. This means that they will vibrate less rigorously and become more ordered.

Boiling: Boiling is defined as the transition from a liquid state to a gas state, usually when a liquid is heated to its boiling point. The heat energy is transferred to the particles which increases their rate of vibration until they become very disordered- gaseous state.

Condensation:This is the process by which gas is changed into liquid, most easily described with water. When the water vapour cools, it condenses into liquid water. Condensation is the opposite of evaporation, which is when a liquid becomes a gas by being heated it.

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In the comments below, suggest a way that you would explain these processes to your class?

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This article is from the free online course:

Teaching Primary Science: Chemistry

National STEM Learning Centre