CBSE Class 11-science Answered

What is the difference between isothermal and adiabatic expansion in terms of change in heat,change in internal energy,work done,change in volume,pressure and temperature.

Asked by Malik Tariq Ul Islam | 13 Feb, 2011, 09:24: PM

Expert Answer

Dear student,

1. Heat: Adiabatic expansion is an increase in volume while pressure is maintained constant. When this occurs, temperature also increases.

Isothermal expansion is an increase in volume while temperature is maintained constant. When this occurs, pressure decreases.

2.change in internal energy: In adiabatic process, internal energy reduces, Isothermal process, internal energy remains constant.

3.work done: Adiabatic expansion of compressed air produces much less work than isothermal expansion starting from the same conditions

The work done during an adiabatic process is given by,
W = C(v){T1 – T2)

In isothermal process, W= p₀(f_vV₀-V₀)

Suppose that the temperature of an ideal gas is held constant by keeping the gas in thermal contact with a heat reservoir. If the gas is allowed to expand quasi-statically under these so called isothermal conditions then the ideal equation of state tells us that

(311)

This is usually called the isothermal gas law.

Suppose, now, that the gas is thermally isolated from its surroundings. If the gas is allowed to expand quasi-statically under these so called adiabatic conditions then it does work on its environment, and, hence, its internal energy is reduced, and its temperature changes.

	Isothermal Process	Adiabatic Process
1.	In an isothermal process, temperature of the system remains constant.	In an adiabatic process, temperature of the system changes.
2.	In this process, the system exchanges heat with the surroundings.	In this process, the system does not exchange heat with the surroundings.
3.	Total internal energy of the system remains constant (DE = 0).	Total internal energy DE of the system changes.
4.	Total heat content of the system changes (DH � 0).	Total heat content of the system remains constant (DH = 0).
5.	In this process, the system is not thermally isolated.	In this process, the system is thermally isolated.
6.	This process can be made reversible.	This process cannot be made reversible.
7.	In this process, Q = W as DE = 0.	In this process, W = (-) DE as DQ = 0