# Isothermal & adiabatic processes

• Entanglement
In summary, when work is done on an ideal gas, its internal energy increases and some of the work is used to increase the volume of the container. If the walls are movable, then the temperature decreases as a result of the work being done on the gas.
Entanglement
I'll start with what I know: when work is done on an ideal gas its internal energy increases and some of the work is used to increase the volume of the container if the walls are movable, and I know that when a gas does work its internal energy decreases by a value equivalent to F.d, I have been gaining good information about the gas laws for several days so I could advance to low temperature physics, but when I reached the adiabatic and isothermal processes, 8couldn't clearly understand their concepts. I know their definitions because I read it lots of times on the internet, but I can't understand the mechanism of achieving both processes practically.

I hope someone could give me a good explanation with simple clear examples. Thanks

Last edited:
The processes are their definitions. The thermodynamic processes you learn are mathematical idealizations used to help model real physical processes.

If you found the definitions online, then some of the same sources should have also given you examples.
i.e. letting air out of a pressure container (i.e. a pneumatic tire) would realize an adiabatic decompression.
(which is to say the process is "well modeled" by an adiabatic process)

Another common example is the compression stroke in a 4-stroke engine.

Isothermal is usually given as a cylinder with a plunger immersed in a heat bath - pull on the plunger very slowly. But you can also think of boiling water in air or pumping up a tire - slowly.
... the process has to be slow to make sure that heat can flow into the system fast enough to maintain the temperature.

Also see:
http://faculty.wwu.edu/vawter/PhysicsNet/Topics/Thermal/ImportantThermalProcess.html

Since these are common - perhaps you have a problem with the examples, or you do not know how they are physically implemented?

Last edited by a moderator:
Simon Bridge said:
The processes are their definitions. The thermodynamic processes you learn are mathematical idealizations used to help model real physical processes.

If you found the definitions online, then some of the same sources should have also given you examples.
i.e. letting air out of a pressure container (i.e. a pneumatic tire) would realize an adiabatic decompression.
(which is to say the process is "well modeled" by an adiabatic process)

Another common example is the compression stroke in a 4-stroke engine.

Isothermal is usually given as a cylinder with a plunger immersed in a heat bath - pull on the plunger very slowly. But you can also think of boiling water in air or pumping up a tire - slowly.
... the process has to be slow to make sure that heat can flow into the system fast enough to maintain the temperature.

Also see:
http://faculty.wwu.edu/vawter/PhysicsNet/Topics/Thermal/ImportantThermalProcess.html

Since these are common - perhaps you have a problem with the examples, or you do not know how they are physically implemented?
if a container of gas of movable walls was to be placed in a room, and then work is done on the gas, the temperature of the gas increases slightly and some work is used up to increase the volume so the temperature decreases (before thermal equilibrium) the overall result is a decrease or an increase in the temperature??

Last edited by a moderator:

## 1. What is an isothermal process?

An isothermal process is a thermodynamic process in which the temperature of a system remains constant while it undergoes a change in volume or pressure. This means that the system's internal energy remains constant during the process.

## 2. How is an isothermal process different from an adiabatic process?

An isothermal process is different from an adiabatic process in that an isothermal process maintains a constant temperature, while an adiabatic process does not allow for heat transfer between the system and its surroundings. This means that in an adiabatic process, the temperature of the system can change due to changes in volume or pressure.

## 3. What is the equation for an isothermal process?

The equation for an isothermal process is given by the ideal gas law: PV = nRT, where P is the pressure of the system, V is the volume, n is the number of moles, R is the gas constant, and T is the temperature.

## 4. How do you calculate the work done in an isothermal process?

In an isothermal process, the work done is equal to the area under the curve on a pressure-volume graph. This can be calculated by integrating the ideal gas law equation, PV = nRT, over the change in volume.

## 5. What are some real-life examples of isothermal and adiabatic processes?

An example of an isothermal process is the expansion of a gas in a piston-cylinder system at a constant temperature. An example of an adiabatic process is the compression of gas in a tire pump, where the temperature of the gas increases due to the decrease in volume and there is no heat transfer with the surroundings.

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