Ideal gases must satisfy two conditions: the gas particles must occupy negligible volume relative to the container volume, and there must be no attractive or repulsive forces between gas particles. At high pressure, the volume between particles (the "free volume") is actually much less than the container volume. Equally important, when gases are subjected to high pressure, the particles can be close enough to interact.
The Dutch physicist Johannes van der Waals developed an equation to correct for the non-ideal behavior of gases. It's based on the ideal gas law and includes a factor that adjusts P upward to compensate for the decrease in P due to intermolecular attractions in real gases. The van der Waals equation also includes a factor that adjusts V downward, to give a measure of only the free volume in the container by excluding the volume occupied by gas particles. The van der Waals equation is:
The a and b terms are called the van der Waals constants and depend on the identity of the gas. For hydrogen gas, the van der Waals constants are:
Imagine that you have a 1.00 mole sample of hydrogen gas in a 1.00 L container at 0.00
C. Discuss whether you believe hydrogen gas is an ideal gas under these conditions. How do you decide? If you believe the gas is not ideal under these conditions, under what conditions of P, V, or T would the gas behave ideally? And what criteria do you use to decide? Explain your reasoning to your classmates, and respond to their explanations.
Scoring
This discussion is worth a maximum of 15 points. You'll get 10 points for participating. Your instructor will give you another 5 points if you post a follow-up comment or question that furthers the discussion.
