If a given mass of a gas is maintained at a constant temperature, ...

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If a given mass of a gas is maintained at a constant temperature, what will decreasing its pressure do?
 
  a. Decrease its volume.
  b. Increase its mass.
  c. Increase its volume.
  d. Decrease its mass.

Question 2

Both a compressed gas cylinder and its regulator are at room temperature with all valves in the off position. After the cylinder is opened and gas begins flowing, you note that the regulator is extremely cold to touch.
 
  Which of the following principles best explains this observation?
  a. Adiabatic compression
  b. Gay-Lussac's law
  c. Joule-Thompson effect
  d. Venturi principle

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Answer to Question 1

ANS: C
If a gas-filled container could be enlarged, the gas would expand to occupy the new volume. Figure 6-19 illustrates the concepts of gas compression and expansion.

Answer to Question 2

ANS: C
The rapid expansion of real gases causes substantial cooling. This phenomenon of expansion cooling is called the Joule-Thompson effect. Adiabatic compression can also occur in gas delivery systems where rapid compression occurs within a fixed container. The rise in temperature caused by this rapid compression can ignite any combustible material in the system. It is for this reason that RTs must take care to clear any combustible matter from high-pressure gas delivery systems before pressurization.