Adiabatic expansion of a real gas

[EgyptianDoc]

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In the adiabatic expansion of a real gas, a decrease in temperature is accompanied by:

A. an increase in the internal energy of the gas
B. a loss of heat by the gas to the surroundings
C. a decrease in the intermolecular forces of the gas
D. a conversion of heat energy to work

What would you say the answer is? I chose D by POE but this is not correct. Wouldn't a decrease in temperature (deviation from ideal behavior) cause the molecules to be closer together and therefore INCREASE the intermolecular forces of the gas? It's C but I'm still not sure why. Where is my logic flawed?

 

[G1SG2]

In the adiabatic expansion of a real gas, a decrease in temperature is accompanied by:

A. an increase in the internal energy of the gas
B. a loss of heat by the gas to the surroundings
C. a decrease in the intermolecular forces of the gas
D. a conversion of heat energy to work

What would you say the answer is? I chose D by POE but this is not correct. Wouldn't a decrease in temperature (deviation from ideal behavior) cause the molecules to be closer together and therefore INCREASE the intermolecular forces of the gas? It's C but I'm still not sure why. Where is my logic flawed?

The gas is expanding-the gas molecules are moving away from each other, and thus there is a decrease in the intermolecular forces of the gas. On the other hand, if you compress a gas, then the molecules are closer to each other and there is an increase in the intermolecular forces of the gas. For D-I think conversion of internal energy to work would've been better wording (since E=-w)-q/heat is 0.

 

[EgyptianDoc]

The gas is expanding-the gas molecules are moving away from each other, and thus there is a decrease in the intermolecular forces of the gas. On the other hand, if you compress a gas, then the molecules are closer to each other and there is an increase in the intermolecular forces of the gas. For D-what heat energy? I think conversion of internal energy to work would've been a better answer choice for D (since E=-w).

Thank you. GChem is not my cup of tea. I misread the question but it makes perfect sense now. D does sound ******ed but this question threw me off. If I narrow it down to two questions and I have no idea, I usually pick the bottom answer. Thanks for the help. 🙂

 

[G1SG2]

Thank you. GChem is not my cup of tea. I misread the question but it makes perfect sense now. D does sound ******ed but this question threw me off. If I narrow it down to two questions and I have no idea, I usually pick the bottom answer. Thanks for the help. 🙂

No problem, but when in doubt, pick C! 😀

 

[Hemichordate]

I have a related question.

In EK, it says that the same amount of the same substance can have an amount of energy and be at different temperatures. But how can that be? I thought if you have add energy to something, you increase the molecules in that solution, thus heating it up. But if you have the same energy in both compounds, why wouldn't the temp remain the same?

 

[letaps]

i am guessing that A and B are wrong because the process is adiabatic, so internal energy and heat loss is not a factor...is that correct?

 

[matth87]

i am guessing that A and B are wrong because the process is adiabatic, so internal energy and heat loss is not a factor...is that correct?

Adiabatic - heat is not transferred
Heat loss is not a factor
Energy is still affected due how every the volume of the container is changing
(delta)E = -P(delta)V

In the adiabatic expansion of a real gas, a decrease in temperature is accompanied by:

A. an increase in the internal energy of the gas
A. If your gas is expanding your volume is increasing, you are losing energy.
B. a loss of heat by the gas to the surroundings
B. Heat is not transferred, this is the definition of adiabatic.
C. a decrease in the intermolecular forces of the gas
C. Correct, expanding gases have their gas particles further away from each other so the intermolecular forces between them are decreased.
* You can also think of it like this, expanding gases cool, compressed gases warm up. If you increase the temperature you are increasing the kinetic energy of the molecules and increasing the intermolecular forces. If you decrease the temperature you are decreasing the kinetic energy of the molecules and decreasing their intermolecular forces.
* You can also think about it like the forces that each molecule is exerting on each other. F = G(m1)(m2)/r^2 or F = K(q1)(q2)/r^2, by increasing the distance between molecules we decrease their forces they exert on each other.
D. a conversion of heat energy to work
D. No heat energy is converted to work, there is no heat transfer.

 

[Hemichordate]

So we're saying that the expansion of the gas is doing no work?

 

[matth87]

So we're saying that the expansion of the gas is doing no work?

(delta)E = q + w
q = 0
work = -P(delta)V

If the gas is expanding delta(v) = positive. The gas is doing work. Energy is leaving the system. The work is negative.

 

[bball]

So in that passage (TPR Diag 6, Passage 1), it states "as the distance between the molecules increases, the potential energy of molecules also increases." I don't get why this is true. Isn't the formula for potential energy such as that radius (distance) and potential energy are inversely related?

Also in the passage is the statement that "since the system is isolated from the surroundings, total energy must remain constant." Does this imply that the system is isothermal (since deltaU = 0), as well as adiabatic?

 

[bball]

anyone?