In this task, you are given a question and an answer, you would be asked to create the sentence based on the Question-Answer provided. It should be contained within the Question-Answer provided.

Q: Question: Expansion of a gas into a vacuum is irreversible because the external pressure is measurably less than the internal pressure of the gas, and no states of what exist? Answer: equilibrium

A: Expansion of a gas into a vacuum is irreversible because the external pressure is measurably less than the internal pressure of the gas, and no states of equilibrium exist.
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Q: Question: What are reversible physical changes in matter called? Answer: changes of state

A: Changes of state are reversible physical changes in matter called.
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Q: Question: A fundamental particle of matter, protons and neutrons are made of these? Answer: quarks

A:
Protons and neutrons are made of quarks, which are fundamental particles of matter.
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