An ideal gas is allowed to expand both reversibly and irreversibly in an isolated system.
An ideal gas is allowed to expand both reversibly and irreversibly in an isolated system. If Ti is the initial temperature and Tf is the final temperature, which of the following statements is correct?
(a) (Tf irrev > (Tf )rev
(b) Tf > Ti for reversible process but Tf = Ti for irreversible process
(c) (Tf )rev = (Tf )irrev
(d) Tf = Ti for both reversible and irreversible processes.
3 Answers
(a) : If a gas was to expand by a certain volume reversibly, then it would do a certain amount of work on the surroundings. If it was to expand irreversibly it would have to do the same amount of work on the surroundings to expand in volume, but it would also have to do work against frictional forces. Therefore the amount of work have greater modulus but –ve sign.
Wirrev. > Wreve.; Tfirrev. > Tfrev.
Correct option(a) (Tf) irrev > (Tf )rev
Explanation:
ln an ideal gas, there are no intermolecular forces of attraction.
Hence, Tf = Ti for both reversible and irreversible processes.
Correct option (D) (Tf) irrev > (Tf) rev
Explanation:
In isolated system, the expansion of gas is carried out adiabatically. Since heat exchange between system and surrounding is not possible i.e. q = 0 and secondary wrev is always greater than wirr- therefore for reversible process there must be comparatively higher decreases in internal energy i.e. ΔU for reversible process will be more negative. Hence, final temperature in reversible process will be smaller than irreversible process.