Sapling #6 Week 5/6

[Maaria Abdel-Moneim 2G]

Hello, I am having trouble with number 6 on the sapling the question says:
A particular container holds 3.30 mol of neon gas. The volume of this container can be altered by sliding a piston in or out. The volume is changed from 8.40 L to 4.70 L while at the same time the temperature is changed from 272 K to 1.50×10^2 K.

The molar heat capacity, CV,m, for neon is 12.47 J/(mol · K). Assume that this value will not change over the given temperature range.

What is the change in entropy for the gas?

I am calculating the first change in entropy by doing 3.30*12.47*ln(4.7/8.4) and then I am calculating the second change in entropy by doing 3.3*12.47*ln(150/272) and then I am adding them together. The feedback just keeps telling me to pay attention to the signs of the entropy change however I am getting negative values for both which is correct with the explanation.

[Adalia 3E]

For your first calculation, I think you used the molar heat capacity rather than the gas constant. I think the feedback referring to the sign of the result isn't specific to your answer.

[Olivia Yang 3J]

So your first calculation should be the equation mol*R*ln(v2/v1) you multiplied by the CV,m in the first equation when it should have been the R constant, 8.314 J/K*mol. Your second calculation should be Cv,m*ln(T2/T1). Once you do these two calculations then you should add them together to get the total Chang win entropy.

[Maaria Abdel-Moneim 2G]

So your first calculation should be the equation mol*R*ln(v2/v1) you multiplied by the CV,m in the first equation when it should have been the R constant, 8.314 J/K*mol. Your second calculation should be Cv,m*ln(T2/T1). Once you do these two calculations then you should add them together to get the total Chang win entropy.

When do we know when to use the gas constant in the delta S equation?

[Adalia 3E]

We use the gas constant when calculating the change in enthalpy relating to a change in temperature