Which of the following systems could be reasonably modeled as reversible?

Question

A. A tub of water is initially at 350 K, but gradually cools to the ambient temperature of 300 K.
B. An ice cube gradually melts in a freezer that has been accidentally set to 1 K above the normal freezing point temperature.
C. You walk outside in a light snow and your skin dissipates heat.
D. After a storm, a drier front (same temperature, relative humidity of 57 %) moves through, producing fog.
E. None of these can be plausibly modeled as reversible.

Answer 1

A. Incorrect. 50 K is a significant driving force. While it cools “gradually,” this is not enough to claim reversibility. The driving forces must be negligible throughout the entire duration of the process.
B. Correct. The thermal driving force here is 1 K, which is small enough to be plausibly reversible.
C. Incorrect. If the snow isn’t melting, it must be at most 273.15 K. Your skin should be at approximately 310 K. This difference (over 30 K) is much too large for the heat transfer to be considered reversible.
D. Incorrect. During a rainstorm, the relative humidity should be about 1 (100%). A humidity difference of 43 % is significant and this is not reversible. While in most of this problem we have been talking about reversibility in terms of heat and temperature, if ANY driving force is significant, the process is not reversible.
E. Incorrect. One of these systems could be considered reversible.
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