Is it generally good to keep the hands as straight as possible while playing the piano? I've noticed that If I try to turn my hand at the wrist to cover the shape of an arpeggio or a chord or any particular figure really, that it causes sever tension for my whole hand. thanks
Yes, that's rotation. With your arm in playing position, your forearm should rotate as if your hand is turning a doorknob. The elbow should not be moving in and out as in a chicken dance.