Thermal equilibrium

1. Dec 4, 2008

snoopygal327

1. The problem statement, all variables and given/known data
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?

2. Relevant equations
$$\Delta$$Eth= Q + W

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