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Homework: Phases of Matter

Answer all items using a complete sentence in your best, most professional writing style. Write definitions in such a way that someone your age who is not taking chemistry would understand it. Do not “Google” the answers: use the text you were given to find the answers to the questions.

Define the following terms:

  1. Solid
  2. Liquid
  3. Gas
  4. Phase change
  1. Temperature
  2. Heat
  3. Molecular stickiness

Answer the following questions with grammatical and complete English sentences.

  1. Can a solid be easily compressed? How about a liquid? A gas? For each case, explain your answer.
  2. Do molecules change size or shape when a substance changes phase (from solid to liquid to gas)? Explain.
  3. Why are gases so much lower in density than liquids?
  4. What is the relationship between temperature and the phase of matter?
  5. Pick the true statement from each pair. For each incorrect sentence, explain why it is wrong.
      1. Solids and liquids form because molecules get stickier when they get colder.
      2. Solids and liquids form because at low temperatures they slow down enough that their stickiness can hold them together.


      1. Gases are compressible because the molecules or atoms of the gas get smaller when the gas is pressurized into a smaller container.
      2. Gases are compressible because when put in a smaller container there is simply less empty space between the atoms or molecules of the gas.


      1. Particles in a solid are in constant motion but cannot move from their position.
      2. Particles in a solid are in constant motion and shift position frequently.


      1. Adding heat makes atoms or molecules move faster. If they move fast enough they break the weak bonds connecting the molecules to each other.
      2. Adding heat makes atoms or molecules less likely to stick together because the stickiness force gets weaker at a higher temperature.


  6. Desribe what happens to the molecules of a solid when it changes from a solid to a liquid. Think about both their motion and their degree of stickiness in your answer.
  7. Desribe what happens to the molecules of a liquid when it changes from a liquid to a gas. Think about both their motion and their degree of stickiness in your answer.
  8. What is between the particles of a gas? Draw a picture of a gas at the molecular level before you write your answer.
  9. When liquid methane (chemical formula, CH4) boils it forms bubbles close to the source of heat which rise up to the top of the liquid and pop. What phase of matter is inside the bubbles? What substance or substances are inside the bubbles? Again, draw a molecular-scale picture before you write your answer.
These questions can be answered after reading notes about the Classification of Matter and Phases of Matter
and the Modeling the Molecular Level Activity
See also: Homework: Elements, Compounds and Mixtures After this basic review sheet try the Writing for Understanding activity.
Phases of Matter with the PhET simulator
Last updated: Aug 20, 2019
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