[fl0raliessc]

Hello,

I was wondering if someone could check my answer for this multiple-choice question? My work is shown below it.

Which statement below is not upheld by the second law of thermodynamics?

A. The change of entropy of the universe is always positive.
B. The entropy of a perfect crystal at 0 K is zero.
C. Machines always waste some energy.
D. A machine is never 100% efficient.
E. All of these

My work:
The second law states that “mechanical work can be derived from a body only when that body interacts with another at a lower temperature; any spontaneous process results in an increase of entropy.” Also, “when energy is transformed, it becomes less useful; every process increases the disorder of the universe; no process is 100% efficient”, and “dG = dH - TdS where dG is the change in Gibbs' Free-Energy and dS is the change in entropy. The second law of thermodynamics states that for a reaction to be 'spontaneous', dG must be negative overall. Another way of stating this is that for a reaction to be spontaneous, the overall entropy increase must be positive.”

D upholds the 2nd law because it states: A machine (or process) is never 100% efficient. B does not uphold to the 2nd law because it is the third law of thermodynamics. Although C is true, it doesn’t uphold to the second law of thermodynamics. Since the second law states that for a reaction to be spontaneous, overall entropy increase is positive so A upholds the second law.
My answer for this question therefore is B and C. But I am leaning more toward B since it describes the third law of thermodynamics. Is this correct?

Thanks for your time!

[priya22]

yes , You are correct. Statement B is the third law of thermodyanamics

[Donaldson Tan]

B does not uphold to the 2nd law because it is the third law of thermodynamics.

The Second Law of Thermodynamics describes processes (or the change in state). Clearly (even if you don't know the second law), it is not applicable for statement B.

you are correct :thmbup: