Hot air becomes cooler as it rises appreciably. Why?

1.	Hot air becomes cooler as it rises appreciably. Why?
Answer» As hot air rises up, it reaches region of reduced pressure. The air suffers adiabatic expansion. From first law of thermodynamics, ∆Q = ∆U + ∆W For adiabatic process, ∆Q = 0 ∆U + ∆W = 0 Since, ∆U becomes negative. Therefore, air becomes cool.

Answer»

As hot air rises up, it reaches region of reduced pressure. The air suffers adiabatic expansion.

From first law of thermodynamics,

∆Q = ∆U + ∆W

For adiabatic process,

∆Q = 0

∆U + ∆W = 0

Since, ∆U becomes negative.

Therefore, air becomes cool.

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Hot air becomes cooler as it rises appreciably. Why?

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