1.

Which one of the following equations does not correctly represent the first law of thermodynamics for the given process

Answer»

Isothermal process : Q = - w
Cyclic process : q = - w
Isochoric process : `DeltaE = q`
Adiabatic process : `DeltaE = - w`

Solution :In adiabatic process, no HEAT is allowed to enter or leave the system, i.e. q = 0
Substituting this value in first law of thermodynamics,
`DeltaE=q+W`, we get `DeltaE=W`
In adiabatic expansion, work is DONE by the system on the surroundings hence W is NEGATIVE. According `DeltaE` is also negative, i.e. internal energy decreases.
In adiabatic compression, W is positive, `DeltaE` is also positive.


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