alone可以作形容词,但是只做表语,不用做定语.
He was alone in the house.
也可以做副词.He came alone.是‘独自’的意思,不含感情色彩
lonely既可以作定语,也可以作表语.
作表语是‘寂寞’、‘孤立’的意思,一般指人孤独寂寞；作定语指地方荒无人烟,有浓厚的感情色彩
She lives alone ,but she doesn't feel lonely.
She felt lonely when she was left alone.
a lonely place