Question

Consider a gas placed in cylinder that has a movable piston.

(a) If the piston moves out so as to increase the volume of the cylinder, identify the system and surroundings (which one is the system and which one is the surroundings).

(b) Will the sign of the work of the system be positive or negative? What about the surroundings?

(c) Describe in which direction the work is "flowing", i.e. is it going from the system to the surroundings or vice versa?

Answer 1

a) as per thermodynamics definition, part of the universe under consideration of study is called a system, in this case, cylinder along with piston is system and remaining part of the universe is surrounding.

b) for the system, the sign of work will be negative(-) because there is an expansion and when there is an expansion of the gas, the system does work on the surrounding, hence for the system it is negative and for the surrounding it is positive (+).

c) as there is an expansion, and the system is doing work on the surrounding. Therefore, work is flowing from system to surrounding.