How can temperature change without heat exchange in an adiabatic process?

[Kaushik]

TL;DR

How is to possible to change the temperature without exchange of heat?

How is to possible to change the temperature without exchange of heat?
Could you please give me an example?

I know it is possible to keep the temperature constant while there is exchange of heat. This is possible when the heat supplied is consumed/lost to the surrounding.

But how is it possible to prevent a system from exchanging heat with the surrounding even when when change in temperature is noticed?

 

[Borek]

What if the heat is just produced in the process?

In practice there are no purely adiabatic processes. With good insulation and if the process is quick enough heat exchange can be negligible.

 

[Kaushik]

What if the heat is just produced in the process?

In practice there are no purely adiabatic processes. With good insulation and if the process is quick enough heat exchange can be negligible.

So what you are saying is that the heat produced is still within the system? Only then we can consider there is no exchange of heat between the surrounding and the system.
But when there is change in temperature won't there be exchange of energy between the surrounding and the system? When temperature is changed, then to attain thermal equilibrium won't the energy be exchanged?

 

[Borek]

But when there is change in temperature won't there be exchange of energy between the surrounding and the system?

Please reread what I wrote, I addressed specifically this problem in my post.

 

[Kaushik]

Please reread what I wrote, I addressed specifically this problem in my post.

So what you are saying is that there is heat exchange taking place but it can be negligible in the presence of good insulation. Isn't? But if the heat exchange is negligible then the change in temperature of the system should also be negligible right?

 

[Borek]

But if the heat exchange is negligible then the change in temperature of the system should also be negligible right?

Explosion is so fast it can be treated as adiabatic - yet the temperature goes up pretty fast. Think where is the source of heat.

That's not the only way of heating something without exchange of heat. For example: do you know how diesel engine works?

 

[Kaushik]

Explosion is so fast it can be treated as adiabatic - yet the temperature goes up pretty fast. Think where is the source of heat.

That's not the only way of heating something without exchange of heat. For example: do you know how diesel engine works?

So we can increase the temperature of the system without exchange of heat by increasing the Kinetic energy of the molecules by some other means? Isn't?
I read the following examples:

• The kinetic energy of the molecules can be increased by applying pressure due to which the temperature increases without exchange of heat. Is it?
• In a microwave the food is heated by the help of electromagnetic with high frequency that increase the kinetic energy of the molecules and hence increasing the temperature.

Are these the examples where the body is heated without exchange of heat?

 

[Kaushik]

Think where is the source of heat.

That's not the only way of heating something without exchange of heat. For example: do you know how diesel engine works?

When I saw the working of the diesel engine, the input air is compressed due to which the temperature and the pressure increases. Then a suitable atomized chemical is brought in contact with the compressed air (high temperature). As soon as it comes in contact, it vaporizes and explodes. There is a rapid increase in temperature. Here, is the source of heat from the increase in kinetic energy (due to a sudden change in pressure) of the chemical that comes in contact with the hot compressed air?

 

[Borek]

Here, is the source of heat from the increase in kinetic energy (due to a sudden change in pressure) of the chemical that comes in contact with the hot compressed air?

There are two phases here.

In the first, gas is compressed - this is one way of changing the temperature without adding heat, by doing work on the gas.

In the second there is an exothermic chemical reaction - no heat added from the outside, but reaction produces heat, so the gas heats itself.

I read the following examples:

• The kinetic energy of the molecules can be increased by applying pressure due to which the temperature increases without exchange of heat. Is it?
• In a microwave the food is heated by the help of electromagnetic with high frequency that increase the kinetic energy of the molecules and hence increasing the temperature.

Are these the examples where the body is heated without exchange of heat?

Yes, these are perfectly valid, but I would start the list with the probably most common process, the one involving release of the chemical energy.

 

[Kaushik]

In the first, gas is compressed - this is one way of changing the temperature without adding heat, by doing work on the gas.

In the second there is an exothermic chemical reaction - no heat added from the outside, but reaction produces heat, so the gas heats itself.

Oh ok! So this is how there is change in temperature without exchange of heat between the surrounding and the system in Adiabatic processes.
The change in kinetic energy of the molecules can be caused by doing work on the molecules. I have read that there are two mode of energy transfer. One being through heat and the other through work. Is it?

 

[Chestermiller]

Oh ok! So this is how there is change in temperature without exchange of heat between the surrounding and the system in Adiabatic processes.
The change in kinetic energy of the molecules can be caused by doing work on the molecules. I have read that there are two mode of energy transfer. One being through heat and the other through work. Is it?

Yes. That's correct. Haven't you ever pumped up a bike tire, and felt the tire become hot? You are doing work to compress the gas, and this work is translated directly into an increase in internal energy of the gas. There is no heat transfer required.

 

[DrDu]

Today we don't think of heat as something which is conserved. Hence it makes no sense to speak of the heat content of a body. What is conserved is internal energy.
Whether in a process heat is flowing over the boundary or not also depends on the choice of the boundary.

The paradigmatic process where temperature changes although there is no heat flow over the boundary is the canon drilling experiment of Lord Rumford. He could show that mechanical energy can give rise to temperature increase of the canons (approximately adiabatic).