1-21 Using the nomenclature of similar to that in the previous problem, characterize the following processes.

(a) The temperature of a gas, enclosed in a cylinder provided with a frictionless piston, is slowly increased. The pressure remains constant.

(b) A gas, enclosed in a cylinder provided with a piston, is slowly expanded. The temperature remains constant. There is a force of friction between the cylinder wall and the piston.

(C) A gas enclosed in a cylinder provided with a frictionless piston is quickly compressed.

(d) A piece of hot metal is thrown into cold water. (Assume that the system is the metal which neither contracts nor expands.)

(e) A pendulum with a frictionless support swings back and forth.

(f) A bullet is stopped in a target.

Solution

(a) The temperature of a gas, enclosed in a cylinder provided with a frictionless piston, is slowly increased. The pressure remains constant.

Pressure remains constant implies isobaric process. The temperature slowly increased and the piston being frictionless implies reversibility.

This process is a reversible isobaric process.

(b) A gas, enclosed in a cylinder provided with a piston, is slowly expanded. The temperature remains constant. There is a force of friction between the cylinder wall and the piston.

Temperature constant implies isothermal. The existence of a force of friction removes the possibility of being reversible, the slow expansion implies quasi-static. Note: quasi-static was not mentioned above due to fact that by definition a reversible process must be quasi-static. However a quasi-static process need not be reversible as in this case here.

This process is an irreversible quasi-static isothermal process.

(C) A gas enclosed in a cylinder provided with a frictionless piston is quickly compressed.

The quickly compressed means the process is non-quasi-static and therefore also non-reversible.

This process is an irreversible non-quasi-static process.

d) A piece of hot metal is thrown into cold water. (Assume that the system is the metal which neither contracts nor expands.)

Since the metal neither contracts nor expands, it is a constant volume or isochoric process. It is not possible to remove the metal from the water and have it heat up again, so it is clearly irreversible.

This process is an irreversible non-quasi-static Isochoric process.

(e) A pendulum with a frictionless support swings back and forth.

Frictionless implies reversibility, lack of mention of other things, does imply constant temperature. Hard to see how pressure or volume can be included.

This process is a reversible Isothermal process.

(f) A bullet is stopped in a target.

Clearly it is not possible to get the bullet to back out of the target so the process is irreversible. Once again, hard to imagine how to include pressure or volume for this system.

This process is an irreversible non-quasi-static process.