Entropy Change in Pumped Air: Increase or Decrease?

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SUMMARY

The discussion centers on the entropy change when air is pumped into a tire. While the initial assumption is that entropy decreases due to gas molecules being closer together, the consensus is that overall entropy increases due to heat released by the compressor. Inside the tire, although the volume decreases, the increase in the number of gas molecules and their increased motion contributes to a net gain in entropy. Thus, while localized entropy may seem to decrease, the overall system experiences an increase in entropy.

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  • Basic knowledge of heat transfer and its effects on gas molecules.
  • Concept of molecular motion and its relation to entropy changes.
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erjkism
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i was just wondering if the entropy increases or decreases when air is pumped into a tire. my guess is that it would decrease because the gas molecules would be closer together. am i correct?
 
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In a way, I suppose. Overall, the entropy has to increase, but that can be expressed by the heat released into the atmosphere by the compressor. I guess that it decreases inside the tire.
 
I'm guessing there's a gain in entropy inside the tire as well. Increasing the pressure is equivalent to increasing heat. On the other hand, the maximum number of positions occupiable by gas molecules has to decrease, but you aso have more gas molecules.

I'm sure this is a common question.
 
I was kind of wondering about the heat issue as well, and I really don't know what to make of it. The molecules are more restricted in their range of motion, but they move faster. I don't know whether that counts as an increase, a decrease, or neutrality. :confused:
 
Sounds like neutrality to me. In a square box, any increase in no. molecules should surely be balanced out by the decrease in volume.
 
what about just the inside of the tire. disregard the heat from the compressor, and instead consider the inside of a tire going from deflated to inflated.
 

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