Young Marx had concept of ALIENATION. Marx believed that Capitalist is an "instrument of bourgeoisie" and is unable to favour worker. Since economic condition of workers become poor, they lose Human essence and become alienated.
Human essence, as per Marx, lies in WORKING. Work is for own welfare, earning livelihood (existence) and showing creativity and innovation, But in capitalist society, man becomes cog in the wheel. He loses individual initiatives and thus Human essence.
Marx connects this loss of essence to Alienation which occurs at different levels.Man becomes Alienated from his labour as capitalism demands working for Market and not for self.
Then working continuously for-profit motive creates gap not only between Labour class among each other’s but also, bourgeois class. Finally, the man is unable to use his creativity which makes life monotonous. This cause Alienation from self.
Marx tries to awaken the worker class by saying that "Idea is false consciousness" and workers should unite to lose their chain and come out of Alienation by bringing Social Revolution.