Question

1) What is held constant with each of these processes, and what type of boundary wall would be required to achieve each of them? a) isochoric b) isothermal c) isobaric

Answer 1

(a)

Isochoric process: It is a thermodynamic process in which the system undergoes a change in pressure and temperature at constant volume.

In this case, the heat absorbed by the gas goes entirely to change its internal energy and its temperature. As heat is supplied at constant volume, its utilized only to increase the internal energy of the gas.

(b)

Isothermal process is a process in which a system undergoes physical changes in which temperature remains constant by the exchange of heat energy with surroundings

Boundary conditions:

For the case of mass of gas in a conducting cylinder fitted with movable friction-less piston:

The cylinder should be in good thermal contact with surroundings and they must good conductors of heat. The surroundings should allow heat exchange with gas in cylinder to keep temperature constant. Moreover, the process should be quasi static.

(c)

In Isobaric process, the system undergoes a change in volume at a constant pressure by exchange of heat energy with surroundings.

In this case, the fraction of heat supplied at constant pressure is used for change in internal energy and for doing external work.

Example: Expansion of gas in a cylinder with freely moving piston.