Seeking advice from experts on thermodynamics problems
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For example: In a room, under standard conditions, the temperature is generally higher at the top than at the bottom. The usual explanation is that as the temperature rises, some gases expand more significantly, resulting in a lower density and thus an increase in altitude; while other gases expand less, leading to a higher density and thus a decrease in altitude. But what is the fundamental reason behind it?
People strive to reach higher places, and water flows toward lower levels; essentially, systems tend to move toward states that are more stable and have less disorder, in accordance with the principle of entropy increase
"Generally speaking, it’s uncertain whether the statement that the temperature is higher above than below is true. Assuming it is true, one possible explanation is that due to gravity, there are more molecules in the lower part compared to the upper part; thus, the intermolecular gravitational forces are weaker, the molecular kinetic energy is higher, and the temperature is greater. It doesn’t seem very reliable
Theoretically, as you said, the expansion of gases when heated and contraction when cooled is quite noticeable. When only natural convection is considered, hot air has a lower density and tends to rise upward, while cold air has a higher density and tends to sink downward. However, in practice, other factors also need to be taken into account; for example, the heat source during the day comes from the sun above, while at night it comes from the ground. Looking at it from a larger scale as well, from Earth’s perspective, the higher the altitude, the lower the actual temperature; above 4500 meters, that area is essentially the snow line. In engineering design, there is a similar situation: for example, the natural suction force of a chimney arises from the temperature difference between its upper and lower ends. The temperature at the top is lower and the volume is smaller, while the temperature at the bottom is higher and the volume is larger; this creates a negative pressure that draws air upward. After all, it is the system inside the house that limits certain conditions. It can’t be generalized.
Take a chimney as an example: there is negative pressure inside the chimney, while the external atmospheric pressure remains constant. The external pressure is greater than that inside the chimney, so why can smoke still be drawn out?
Sir, please explain in detail, preferably by analyzing it from the perspective of force application at a microscopic level\ud83d\ude01
Gas molecules undergo Brownian motion; the comparison is made between the effect of different molecular weights under given conditions and that of Brownian motion.