✔ 最佳答案
Q: Am I correct if I say temp. of a closed gas system increase ,heat must be gained ?
You have already said that the system is a closed one, there is no heat gain or loss from the system. The increase in temperature is not coming from heat flows from outside the system.
Q: If true,how to explain in the adiabatic process,heat (gained/lost)=0 but temp of closed gas system can still increase or decrease by work done?
The heat comes from the internal energy of the gas.
From the 1st law of dynamics dQ = dU + dW
for a closed system, dQ = 0, hence
dU = -dW
That is, compressing the gas (the gas does -ve work) leads to an increase of internal energy, thus an increase of temperature.
Expansion of the gas on its own (the gas does +ve work) causes a decrease of internal energy and decrease of temperature.
2011-04-09 14:41:55 補充：
Of course, in an open system, the temperature of the gas is greatly affected by the temperature of the environment. There could be heat flow in or out from the gas.
