Changes of State Flashcards

All 6 cards in this deck

What is sublimation?

A change of state from solid directly to gas (or gas directly to solid), without becoming a liquid.

What happens to the mass of a substance when it melts, boils, condenses or freezes?

Mass is conserved — it stays the same.

Why are changes of state physical changes rather than chemical changes?

They are reversible — the material recovers its original properties if the change is reversed, and no new substance is formed.

What does a flat (horizontal) section on a temperature–time heating graph show?
e.g. a plateau at 0 °C while ice is heated

A change of state is happening: the temperature stays constant while energy is supplied — here the ice is melting.

When a substance is melting or boiling, why does its temperature stay the same even though energy is still being supplied?

The energy is used to overcome the bonds holding the particles together, so none goes into making the particles move faster and the temperature does not rise.

When a substance is condensing or freezing, why does its temperature stay the same?

As the particles bond together they give out energy, which stops the temperature dropping until all of the substance has changed state.