Thermal Equilibrium in a Locked Cylinder Immerse

[snoopygal327]

Homework Statement

A cylinder with its piston locked in place is immersed in ice water. After the gas comes to thermal equilibrium with its surroundings, the piston is unlocked and moved inward very slowly, in such a way that the gas always maintains thermal equilibrium with the ice water. Does the temperature of the gas increase, decrease, or stay the same? Is the heat transferred to the gas positive, negative, or zero?

Homework Equations

$$\Delta$$E_th= Q + W

The Attempt at a Solution

I know this should be easy, but I keep getting confused. Does thermal equilibrium mean that $$\Delta$$E_th=0 or that Q=0? I know that the work done on the gas is positive.

 

[jbsteele]

I think the answer to both questions is that the temperature stays the same and the heat transferred to the gas is zero.

 

[thomate1]

In this scenario, the temperature of the gas will decrease, as it is in contact with a colder environment (ice water). Since the gas is in thermal equilibrium with its surroundings, there is no net transfer of heat (Q=0). However, work is still being done on the gas as the piston is moving inward, so there is a positive value for work (W>0). This means that the change in internal energy (\DeltaEth) is negative, indicating a decrease in temperature.

Thermal equilibrium means that there is no net exchange of heat between the gas and its surroundings. This does not necessarily mean that there is no change in internal energy, as work can still be done on the gas. In this case, since the gas is in a closed system and there is no net exchange of heat, the change in internal energy is equal to the work done on the gas (assuming no other forms of energy transfer). Therefore, in this scenario, \DeltaEth= W > 0.