Reduce the volume of a gas.How much heat, how much pressure?

In summary: If the compression is done quickly, the gas will heat up and the pressure will increase rapidly. As it cools off to ambient temperature, the pressure will drop slightly due to the decrease in temperature and the relationship PV=nRT. This is known as the adiabatic process and follows the adiabatic condition PV^γ = K, where γ is the ratio of specific heats at constant pressure and constant volume. This process assumes a reversible compression, but in the real world, adiabatic compressions are very close to reversible if temperature and pressure are uniform throughout the volume of gas. The increase in temperature in this process is due to the work being done on the gas, which adds energy to the molecules through collisions with the moving
  • #1
peanutaxis
24
3
If I, say, half the volume of a[n ideal] gas adiabatically, how on Earth can I tell how much the pressure will increase and how much the temperature will increase? PV=nRT

Also, by what mechanism does the temperature increase? What would convince the molecules to move any faster? I can see why the pressure would increase due to a larger number of collisions per unit area per unit time, but why would the average speed of a molecule increase?

Last question. If I compress a gas very quickly and it gets hot, and then let it cool off to ambient, will the pressure climb rapidly as I compress it and then drop a little as it cools due to PV=nRT?thanks!
p
 
Science news on Phys.org
  • #2
peanutaxis said:
If I, say, half the volume of a[n ideal] gas adiabatically, how on Earth can I tell how much the pressure will increase and how much the temperature will increase? PV=nRT
If it is compressed adiabatically, one has to use the adiabatic condition: ##PV^\gamma = K##, K being a constant and ##\gamma = \frac{C_p}{C_v}##, i.e. the ratio of specific heats at constant pressure and constant volume. This assumes a reversible compression. In the real world adiabatic compressions are very close to reversible if T and P are fairly uniform throughout the volume of gas during the compression process.

Also, by what mechanism does the temperature increase? What would convince the molecules to move any faster? I can see why the pressure would increase due to a larger number of collisions per unit area per unit time, but why would the average speed of a molecule increase?
Since you are doing work on the gas with no heat flow into or out of the gas, the first law tells you that internal energy has to increase. As the walls move in, the moving walls add energy to the molecules that collide with it.

Last question. If I compress a gas very quickly and it gets hot, and then let it cool off to ambient, will the pressure climb rapidly as I compress it and then drop a little as it cools due to PV=nRT?
Yes.

AM
 

1. How do you reduce the volume of a gas?

To reduce the volume of a gas, you can either decrease the temperature or increase the pressure. This can be achieved by using a variety of methods, such as compression, cooling, or chemical reactions.

2. How much heat is needed to reduce the volume of a gas?

The amount of heat needed to reduce the volume of a gas depends on its initial volume, pressure, and temperature. In general, a decrease in temperature will require less heat compared to an increase in pressure.

3. What role does pressure play in reducing the volume of a gas?

Pressure is directly related to the volume of a gas according to Boyle's Law. This means that as pressure increases, the volume of the gas decreases, and vice versa. Therefore, increasing the pressure can effectively reduce the volume of a gas.

4. Can gas volume be reduced without changing the temperature or pressure?

Yes, it is possible to reduce the volume of a gas without changing the temperature or pressure by using a process called adsorption. This involves the gas being attracted to and sticking onto a surface, effectively reducing its volume.

5. How does reducing the volume of a gas affect its properties?

Reducing the volume of a gas can lead to changes in its physical and chemical properties. For example, the density and pressure of the gas will increase, while the temperature and volume will decrease. This can also cause the gas to undergo phase changes, such as turning into a liquid or solid.

Similar threads

I Compressing gas with piston: reasons for temperature increase?
    • Thermodynamics
Replies
5
Views
2K
I Yet again about (real) gas compression
    • Thermodynamics
Replies
20
Views
1K
I Trying to wrap my head around gas turbine thermodynamics
    • Thermodynamics
Replies
5
Views
594
I Time for a cold volume of air to reach a higher air temperature
    • Thermodynamics
Replies
11
Views
1K
I Focus Problem for Entropy Change in Irreversible Adiabatic Process
    • Thermodynamics
2
Replies
56
Views
3K
A How was the Birch-Murnaghan equation derived for high pressure volume behavior?
    • Thermodynamics
Replies
3
Views
783
B Energy seems to disappear when gas is compressed?
    • Thermodynamics
Replies
3
Views
980
I Questions about my Understanding of Thermodynamics and Statistical Mechanics
    • Thermodynamics
Replies
2
Views
451
I Graphical difference between adiabatic and isothermal processes.
    • Thermodynamics
Replies
1
Views
604
Heat Absorbed by Gas: An Expert Explanation
    • Thermodynamics
Replies
2
Views
1K

Hot Threads

Recent Insights

Back
Top