An adiabatic process is one in which no heat is gained or lost by the system. The first law of thermodynamics with Q=0 shows that all the change in internal energy is in the form of work done. This puts a constraint on the heat engine process leading to the adiabatic condition shown below. This condition can be used to derive the expression for the work done during an adiabatic process.

Index

Heat engine concepts

 HyperPhysics***** Thermodynamics R Nave
Go Back

Index

Heat engine concepts

 HyperPhysics***** Thermodynamics R Nave
Go Back

For an ideal gas consisting of n = moles of gas, an adiabatic process which involves expansion from

 =
 to = =
 at initial temperature = K

With the initial volume and temperature specified, the initial pressure is determined:

 Using , = kPa = x10^ Pa

The detailed behavior of the pressure and volume depends upon the specific heats of the gas:

 Constant pressure = J/mol K
 Constant volume = J/mol K
 The specific heats determine the ratio, =

and then the adiabatic condition can be applied to determine the constant K .

 =

The work done can then be determined:

 = J = x10^ J

The final pressure for the process can be determined from the adiabatic condition:

 = kPa = x10^ Pa

and the final temperature can be obtained from the ideal gas law.

 = K
The specified initial temperature for the work calculation must be in Kelvins, so it must be converted from the other temperature scales.
 = K = °C = °F