Question

A cylinder of gas with a fixed piston is moved from a boiling water bath to an ice water bath. Consider the system is the gas as it comes to equilibrium with the new temperature bath.

1) Is the object is absorbing or giving off heat? Why?

2) Is the object's temperature increasing or decreasing? Why?

3) Is the object's internal energy increasing or decreasing? Why?

4) Is the object is doing mechanical work or having work done on it? Why?

5) Is the object's entropy increasing or decreasing? Why?

Answer 1

1) Since the surroundings are colder, the object will be giving off heat

2) Since Q < 0 and W = 0, ΔU =Q - W < 0. So, internal energy is decreasing, which means temperature is decreasing.

3) Since Q < 0 and W = 0, ΔU =Q - W < 0. So, internal energy is decreasing

4) Since the piston is fixed, change in volume of the system is zero, so mechanical work is zero.

5) Since the object is giving off heat, ΔS = Q/T < 0, i.e. its entropy is decreasing.