障碍 is only a NOUN. 阻碍 can be both NOUN and VERB. 妨碍 is only a VERB. when they're verbs,阻碍 is equivalent to 妨碍. ( the subjective of 妨碍 is often a man.somebody 妨碍 and something 阻碍)

阻碍 and 妨碍 are pretty much the same, and are verbs meaning "to obstruct, to hinder, to block" 障碍 is a noun, meaning: "barrier; obstruction; hindrance; impediment; obstacle" A decent online Chinese <--> English dictionary is http://www.xiaoma.info/

Block: a little stop you when you face a difficult difficult is called a block Obstacle: a variety of means, the most common such as language barrier, is communication problems, or traffic disorder, as the traffic problems Block: hinder to someone's expression, is mainly refers to someone more likely to be a person of another person's behavior or action and bad influence on the expression. Hope to help you, also hope you can pay attention to me, we can communicate with the culture of the language, thank you