Page 21 - York Global Science 6 - Physical Science

Physical Science

Let’s Learn

Materials can change state when they are heated or cooled.

Changes in state are also called physical changes. Physical changes
are reversible because no new materials are made and the particles
themselves do not change. It is just the arrangement and movement of the

particles that are different. When a material is heated, the energy inside it
increases. This makes the particles move more and spread out. This can
cause changes of state like melting and evaporation. When a material is
cooled, the energy inside it decreases. This makes the particles move less,

so they get closer together. This can cause changes of state like freezing
and condensation.

evaporation condensation gas sublimation

freezing

melting

liquid solid

Sublimation is when a solid changes to a gas without going to a liquid
state first. Solid carbon dioxide changes into carbon dioxide gas at room
temperature without changing into a liquid first. Sublimation happens
because heat energy is absorbed so quickly that melting never takes place.

Snow and ice can sublime in the winter months without melting. Because
no particles are lost and no new particles are made, the mass of a material
stays the same in each state. This is called the conservation of mass
theory.

Let’s Reflect

1 Explain what conservation of mass means.

2 What happens to particles during a change of state?

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