When something that is unexpected to happen tends to occur in literature, making the dull and story take an interesting turning point is known as irony.
In Kate Chopin's, "The Study of An Hour", When Josephine inform Mrs. Mallard about the death of her husband we tend to observe her first reaction where she weeps into her sister’s arm and was hard to take. “She wept at once, with sudden, wild abandonment, in her sister’s arms.” In such grief she rushes off to her room to be alone, later it is observed that “But now there was a dull stare in her eyes, whose gaze was fixed away off yonder on one of those patches of blue sky. It was not a glance of reflection, but rather indicated a suspension of intelligent thought.” And the reader see something coming to her and speaks softly “free, free, free!”. This situation can be dramatic as only the reader knows the real feeling of Mrs. Mallard. On the other hand, other characters are not aware of her real feelings. She celebrates it and by the end, she is dead with a heartbreak, wherein, her husband receives the news of Louise's death.
Hence, narrative technique employed by Chopin here is situational irony.
