States of Matter & Phase Changes — Drills · Grade 8 Science

Chapter: Phases of Matter

What these drills covers

By the end of States of Matter & Phase Changes you should be able to:

8 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: solid, liquid, gas, melting point, boiling point, condensation, thermal energy, model, evidence, system boundary, assumption.

Problem 1

In which state are the particles held in fixed positions, vibrating in place?
  1. Solid
  2. Liquid
  3. Gas
  4. Plasma
Answer and explanation

Solid

Solid particles vibrate about fixed positions, which is why a solid keeps its shape.

Problem 2

Changing from a liquid to a gas is
  1. condensation
  2. evaporation
  3. freezing
  4. sublimation
Answer and explanation

evaporation

Evaporation (or boiling) takes a liquid to a gas; condensation is the reverse.

Problem 3

Water freezes at 0 °C and boils at 100 °C at standard pressure. How many degrees Celsius separate the two?
Answer and explanation

100 °C

100 − 0 = 100 °C.

Problem 4

While ice is melting at 0 °C, the temperature of the mixture
  1. rises steadily
  2. falls
  3. stays the same
  4. doubles
Answer and explanation

stays the same

During a phase change the energy added breaks attractions between particles rather than raising temperature, so the reading holds steady.

Problem 5

A sealed flask of gas is heated. Explain what happens to the particles and to the pressure.
Answer and explanation

The particles gain kinetic energy and move faster, so they strike the walls more often and harder. Because the flask is sealed the volume cannot change, so the pressure rises. The number of particles has not changed.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 6

Sublimation is the change from
  1. solid straight to gas
  2. gas to liquid
  3. liquid to solid
  4. solid to liquid
Answer and explanation

solid straight to gas

Sublimation skips the liquid state entirely, as solid carbon dioxide does at room temperature.

Problem 7

A substance melts at −39 °C. A sample sits at −50 °C. How many degrees must it warm to reach its melting point?
Answer and explanation

11 °C

−39 − (−50) = 11 °C.

Problem 8

Explain why a phase change does not change the mass of a sample.
Answer and explanation

A phase change rearranges how particles are held together; it does not create or destroy them. The same particles are present before and after, so the mass is unchanged. In an open container mass can appear to drop only because gas particles have escaped and are no longer being weighed.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

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