Real gases

[Tokspor]

Which of the following is NOT true of a gas at 400 atm and 0 K?

A. The pressure of the gas is always lower than that predicted by the ideal gas law.
B. The extent to which the gas deviates from the ideal gas law depends on the molecules' size and polarity.
C. Intermolecular forces become significant.
D. The ideal gas equation is less accurate under these conditions than at higher temperatures and lower pressures.

A is not true and therefore the correct answer. I thought it was true considering that P(real) < P(ideal) because for real gases, the attractive forces between the molecules pull them away from exerting as strong of a force on the walls.

The text's reasoning is that "when coupled with the effect of excluded volume, no generalization can be made as to whether the actual or ideal pressure would be greater." What might they mean by this? Do they mean "without knowing what the volume is?" If that's the case, don't we also need to consider the volume in order for C and D to be true?

---

Members don't see this ad.

 

[smec]

Which of the following is NOT true of a gas at 400 atm and 0 K?

A. The pressure of the gas is always lower than that predicted by the ideal gas law.
B. The extent to which the gas deviates from the ideal gas law depends on the molecules' size and polarity.
C. Intermolecular forces become significant.
D. The ideal gas equation is less accurate under these conditions than at higher temperatures and lower pressures.

A is not true and therefore the correct answer. I thought it was true considering that P(real) < P(ideal) because for real gases, the attractive forces between the molecules pull them away from exerting as strong of a force on the walls.

The text's reasoning is that "when coupled with the effect of excluded volume, no generalization can be made as to whether the actual or ideal pressure would be greater." What might they mean by this? Do they mean "without knowing what the volume is?" If that's the case, don't we also need to consider the volume in order for C and D to be true?

I thought A would be true too. BTW, what substance can truly exist as gas at 400 atm and 0 K? Would it not be solid under these conditions if you were to refer to any phase diagram in your textbook?

 

[matth87]

Zero degree Kelvin is the temperature at which all molecular motion halts.

If the is no molecular motion then there is no kinetic energy and there is no pressure. The pressures of both gases will be equal to zero. There for it is not always lower.

 

[thebillsfan]

Zero degree Kelvin is the temperature at which all molecular motion halts.

If the is no molecular motion then there is no kinetic energy and there is no pressure. The pressures of both gases will be equal to zero. There for it is not always lower.

wait, if the pressure of a gas at 0K is zero (pretending that you can have such a gas), then wouldnt the pressure HAVE to lower? its not like you can have a negative pressure at a higher temp

 

[Doctor Mayo]

Zero degree Kelvin is the temperature at which all molecular motion halts.

If the is no molecular motion then there is no kinetic energy and there is no pressure. The pressures of both gases will be equal to zero. There for it is not always lower.

The question says "a gas at 400 atm and 0 K". How do you account for your "no pressure" rationale here?

 

[MCATBear]

Regardless of what n and V are, the ideal gas law will predict 0 P at 0 Kelvin
P = nrT/V or in this case P = 0/who cares. If the ideal gas law predicts a pressure of 0, then A. "The pressure of the gas is lower than that predicted by the ideal gas law" is basically saying "The pressure of the gas is less than 0" which is not true.