Changing states | Year 4 Science PDF Download

Freezing and melting

• Solids, liquids, and gases change their state when they are heated or cooled. 
• This means that they can transform from a solid to a liquid or from a liquid to a gas depending on the temperature.

Heating up a solid

When certain solids are heated, they transition into a liquid state. For instance, substances like wax and ice melt when exposed to heat. The specific temperature at which this change occurs is known as the melting point, typically measured in degrees Celsius (°C).

• The melting point of ice (solid water) is 0 degrees Celsius (0°C).
• Different materials have different melting points. For example, chocolate melts at around 35°C.

Cooling Down a Liquid 

• When a liquid is cooled, it changes into a solid form through a process called freezing. 
• An example of this is when water freezes into ice in puddles on extremely cold days. 
• Freezing occurs at a specific temperature known as the melting point.

Heating Up a Liquid 

• When heat is applied to a liquid, it transforms into a gas through a process known as boiling. For instance, when water is heated in a pan or kettle, it boils and changes into steam. This transformation occurs at a specific temperature called the boiling point. For water, this point is at 100°C, while for ethanol (alcohol), it is at 78°C.
• If water is heated gradually at a temperature below its boiling point, the surface water molecules will evaporate. For example, on a sunny day, water in a puddle may slowly evaporate. Factors like wind or spreading the water thinly across a surface can accelerate evaporation.

Cooling down a gas

• When a gas is cooled, it undergoes condensation, transforming into a liquid. 
• For instance, steam emerging from a boiling pot transitions into condensation on a chilled kitchen window.