الشغل بواسطة الغاز Pressure-volume work

مصطلحات مفتاحية

ملخص

For a gas, work equals change in pressure times a change in volume.
 Work depends on how pressure and volume are changed.

الفلاش 

Work Done by a Gas

 

When a gas expands it does work on its surroundings. That work is equal to the area under the curve on a P-V diagram which describehs that expansion.

 


Isobaric process:

 

Process at constant pressure:

W = F D

W = ( F / A ) ( A D )

W = P ( AD )

W = P (V)

Work = area under the curve on a P-V diagram.

 


 

Work = area under the curve on a P-V diagram -- even if the process is not isobaric.

 


 

 


Isometric processes:

 

Isochoric:

Constant volume:

No work is done in an isometric process.

 


Isothermal process:

 

Process at constant temperature:

We can keep the temperature constant by having the system in contact with a heat reservoir.

 


Adiabatic process:

 

Process with zero heat flow:

Insulated:

The amount of work done will be less than for an isothermal process between the same two volumes. Notice that an adiabat is steeper than an isotherm.

 


Example:

 

W = 2.5 atm-l

Now, what is an "atmosphere-liter"? It is a pressure (atm) multiplied by a volume (liter) so it must be some sort of work or energy. Now, this is just a units conversion question,

W = 2.5 atm-l [ 0.001 m3 / 1 l ] [ 1.013 x 105 Pa / 1 atm ]

W = 253 Pa-m3 [ (N/m2) / Pa ]

W = 253 N-m

W = 253 J

المصدر

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فيديو




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