# B Struggle to understand adiabatic process

1. Mar 25, 2016

### John Pang

I find really confused about the adiabatic process. According to my textbook, adiabatic process is a process in which no heat is allowed to flow into or out of a system.
According to the first law of thermodynamics, change in internal energy=heat added to system- work done by system,so change in Q is equal to -W in an adiabatic process. And change in U=3/2kT.So, if there is work done on a system, the temperature of a system will change even if there is no heat added to the system. This is exactly the part that comfuses me. Why an object can change its temperature without heat adding into it? And work done is also associated with heat. Without heat addition, how is work done possible?

2. Mar 25, 2016

### John Pang

And does this imply that an object may have its temperature unchanged even though there is heat lost from it?

3. Mar 26, 2016

### Staff: Mentor

If you have a gas in a cylinder with a piston, and you move the piston to compress the gas, the face of the piston is exerting an unbalanced force on the gas molecules near the piston face, and is thus doing work on them. So their kinetic energy is increasing. This kinetic energy increase is then transmitted by collisions to the other molecules comprising the gas. So the energy per molecule is increased. This means that the temperature of the gas is higher. This happens even if no heat is added or removed from the gas. And, yes, this does imply that a gas can have its temperature unchanged even it there is no heat transfer to or from the gas.

Chet

Last edited: Mar 26, 2016
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