When two gases are mixed, the entropy of the system increases. This occurs because the mixing process increases the randomness or disorder of the system since the molecules of the gases can spread out and occupy more possible positions and energy states. The increase in entropy reflects the increase in the number of possible microstates available to the gas molecules after mixing compared to when they were separate. Thus, mixing two gases results in a spontaneous increase in entropy due to the greater disorder and expansion of accessible volume for each gas.
