# Isothermal Expansion w/ Equal Pressures

• Mohankpvk
There are two ways to get the gas to expand: (a) increase the outside temperature or (b) decrease the outside pressure. Or you can use combinations of outside pressure and temperature changes, if, at the final state, the volume (calculated from the ideal gas law) is greater than the initial volume.In summary, the gas will not expand isothermally if the initial system pressure is equal to the initial surrounding pressure. However, if the pressure is increased or decreased (or both), then the expansion can occur isothermally.

#### Mohankpvk

In an isothermal expansion of an ideal gas, can the piston be made to expand isothermally if the initial system pressure is equal to the initial surrounding pressure?(In most of the books and video lectures whenever they explain isothermal expansion, they assume initial system pressure to be higher than surrounding pressure.A well known example is a piston cylinder arrangement with weights placed on the piston.They never assume the initial pressures to be equal.)

Mohankpvk said:
In an isothermal expansion of an ideal gas, can the piston be made to expand isothermally if the initial system pressure is equal to the initial surrounding pressure?(In most of the books and video lectures whenever they explain isothermal expansion, they assume initial system pressure to be higher than surrounding pressure.A well known example is a piston cylinder arrangement with weights placed on the piston.They never assume the initial pressures to be equal.)
Why don't you precisely define a focus problem that we can work on together to help you get an understanding of these issues?

Chestermiller said:
Why don't you precisely define a focus problem that we can work on together to help you get an understanding of these issues?
Let us consider a frictionless piston cylinder arrangement containing an ideal gas.Initially the gas(system) inside the arrangement is at atmospheric pressure.The surrounding is the atmosphere.So the piston is at rest.If we heat the cylinder(by placing it in contact with a slightly higher temperature source(infinitesimal temperature difference), can the gas expand isothermally?(If so, please tell me whether the pressure of the gas increases or decreases during expansion and whether the final system pressure value will be higher or lower than the initial value after attaining equilibrium(the piston comes to rest))

Mohankpvk said:
Let us consider a frictionless piston cylinder arrangement containing an ideal gas.Initially the gas(system) inside the arrangement is at atmospheric pressure.The surrounding is the atmosphere.So the piston is at rest.If we heat the cylinder(by placing it in contact with a slightly higher temperature source(infinitesimal temperature difference), can the gas expand isothermally?(If so, please tell me whether the pressure of the gas increases or decreases during expansion and whether the final system pressure value will be higher or lower than the initial value after attaining equilibrium(the piston comes to rest))
is the cylinder horizontal or vertical? If the cylinder is vertical, does the piston have mass, or is it massless?

Chestermiller said:
is the cylinder horizontal or vertical? If the cylinder is vertical, does the piston have mass, or is it massless?
The piston doesn't have any mass.So I think there will not be any difference between the two orientations.

If the cylinder is in contact with a slightly higher temperature source during this scenario, then, in the end, the temperature of the gas will be at the slightly higher source temperature, and the volume will be slightly higher. In other words, not much expansion will happen. The equilibrium pressure of the gas in the end (as well as throughout this "expansion") will be atmospheric.

Mohankpvk
Chestermiller said:
If the cylinder is in contact with a slightly higher temperature source during this scenario, then, in the end, the temperature of the gas will be at the slightly higher source temperature, and the volume will be slightly higher. In other words, not much expansion will happen. The equilibrium pressure of the gas in the end (as well as throughout this "expansion") will be atmospheric.
Thank you.So this means the process cannot be isothermal (i.e. if the initial system and surrounding pressures(before expansion) are equal, the process cannot be an isothermal expansion)I am not really sure whether my inference is right.Please comment on it.

Mohankpvk said:
Thank you.So this means the process cannot be isothermal (i.e. if the initial system and surrounding pressures(before expansion) are equal, the process cannot be an isothermal expansion)I am not really sure whether my inference is right.Please comment on it.
There are two ways to get the gas to expand: (a) increase the outside temperature or (b) decrease the outside pressure. Or you can use combinations of outside pressure and temperature changes, if, at the final state, the volume (calculated from the ideal gas law) is greater than the initial volume.

Mohankpvk

## 1. What is isothermal expansion with equal pressures?

Isothermal expansion with equal pressures is a thermodynamic process in which a gas expands at a constant temperature while experiencing equal external and internal pressures.

## 2. How does isothermal expansion with equal pressures differ from other types of expansion?

In isothermal expansion with equal pressures, the temperature remains constant throughout the process, while in other types of expansion, the temperature may change.

## 3. What are the applications of isothermal expansion with equal pressures?

Isothermal expansion with equal pressures is commonly used in heat engines and refrigeration systems, as well as in gas storage and transportation.

## 4. What is the equation for calculating work done during isothermal expansion with equal pressures?

The equation for calculating work done during isothermal expansion with equal pressures is W = PΔV, where W is the work done, P is the pressure, and ΔV is the change in volume.

## 5. Can isothermal expansion with equal pressures occur in real-life scenarios?

Yes, isothermal expansion with equal pressures can occur in real-life scenarios. For example, when a gas is released from a pressurized container into the atmosphere, the temperature remains constant, and the pressure inside and outside the container is equal.