A reaction is a hot, in-the-moment burst of emotion that's usually driven by our ego (so we're more likely to react when we're disconnected from ourselves).  It might last just a split second before our intuition kicks in and offers some perspective, or it might take over to a point that we act on it.  When we feel crappy after dealing with a situation or person, that's a sign we've reacted rather than responded.  Responding will leave you feeling like you handled things with integrity and respect.