Yes, EQUILIBRIUM is a Scrabble word!

Letter values in Scrabble US: E 1, Q 10, U 1, I 1, L 1, I 1, B 3, R 1, I 1, U 1, M 3.

Is it a valid word?

EQUILIBRIUM is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a stable situation in which forces cancel one another
a chemical reaction and its reverse proceed at equal rates
equality of distribution
a sensory system located in structures of the inner ear that registers the orientation of the head

Also: chemical equilibrium, labyrinthine sense, vestibular sense, sense of balance, sense of equilibrium.