Question

An ideal gas is allowed to expand both reversibly and irreversibly in an isolated system. If T_i is the initial temperature and T_f is the final temperature, which of the following statements is correct?
(a) (T_f  irrev > (T_f )rev
(b) T_f > T_i for reversible process but T_f = T_i for irreversible process
(c) (T_f )rev = (T_f )irrev
(d) T_f = T_i for both reversible and irreversible processes.

Answer 1

(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. 

W_irrev. > W_reve.; T_firrev. > T_frev.