Reading Quiz

Question 1:

We have a microscopic definition of entropy: S =k ln Ω. What is the macroscopic definition of entropy?

Answer:

dS = Q/T
  1. delta S= Q/T
  2. S = Integrate[C_V/T',T',0,T] + S(0) Entropy is the integral with respect to temperature of the heat capacity at constant volume over the temperature. This is the change in entropy between the limits of integration, so S(0) is added to account for any residual entropy at T=0.
  3. The macroscopic definition of entropy is dS = Q/T.
  4. A macroscopic view of entropy is simply that entropy is the thing that increases y Q over T when heat Q enters a system at temperature T.
  5. The macroscopic definition of entropy is deltaS=Q/T.
  6. The macroscopic definition of entropy deals not with multiplicity but with heat flow. When head is added to a substance and thus increases it's temperature, the substance also gains entroy. So it is the thing that increases by Q/T whenever Q enteres a system at T.
  7. An infinitemal change in entropy dS is defined as heat added Q divided by the temperature T while holding volume and N constant and doing no work.
  8. S = Q/T, but it's more useful as ds = dq/T
  9. S=Energy/Temperature
  10. dS=Q/T (Entropy is the thing that increases by Q/T whenever Q amount of heat enters a system of temperature T)
  11. dS=Q/T

Question 2:

In the example on the bottom of p. 95, we find from eq. (3.23) that the entropy of object A decreased. Does this violate the second law of thermodynamics? Briefly explain your anser.

Answer:

This object lost entropy because heat flowed out of it into object B. But the gain in object B's entropy was larger than the loss in object A's entropy, so the overall entropy of the combined system did increase, in accordance with the second law.
  1. No. The entropy of object A decreased by 3 J/K, but the entropy of object B increased by 5 J/K. So for the closed system of objects A and B, the overall entropy increased (by 2 J/K).
  2. The second law says that the TOTAL entropy of an ISOLATED system can't decrease. Object A is not an isolated system (since it's in contact with object B), and the total entropy of A and B increases.
  3. This does not violate the second law of thermodynamics because the entropy was not completely lost from the system of both A and B. The entropy was carried by heat from A into B, and created more entropy in the process.
  4. No, because the total change in entropy of the whole system is +2 J/k (3.23+3.24). You can't consider just each of the object by themselves to constitute a system by itself, since without the contact no heat (and change in entropy) would occur.
  5. No, the entropy of object B increased by a greater magnitude than the entropy of object A increased. This means that the total entropy of the system increased, so the second law of thermodynamics is not violated.
  6. No. Just like everything else the second law refers to the whole process not just one object. If the entropy of something decreses, the entropy of something else increases by that or more amount due to the entropy loss from the first object.
  7. No, entropy actually increases here because the net change in the entire system is -3 + 5 = 2 J/K. Object A did lose entropy because it was cooling, but there is still a net increase.
  8. No, because the second law applies to the "system" and in this case the system is the two objects in thermal equilibrium. Overall, the system moves toward a more probable macrostate and overall the entropy change is positive.
  9. No, system a loses 3 units of entropy, and systemb gains 5, so over all entropy increases by 2 units.
  10. No, because even though entropy is being lost by object A, entropy is also being gained by object B (and in fact, more entropy than was lost). So the second law is not violated since the total entropy of the universe is actually increasing due to this process.
  11. No because the overall entropy of the system will be positive.

Question 3:

What material from the reading or previous classes would you like me to go over in more detail?

Answer:

Your responses below.
  3. I do not quite understand his model that he says doesn't work on page 96-97.
  4. None
  5. This reading seemed to be straight-forward.
  9. none really...
  10. So what exactly is the third law of thermodynamics? Is it 'the entropy of a system goes to zero at zero temperature', or is it 'the heat capacity at constant volume goes to zero at zero temperature', or is there yet another way to state it, perhaps more descriptively?
  11. welp