Reacting

To act or perform a second time; to do over again; to reenact.

To return an impulse or impression; to resist the action of another body by an opposite force

"Every body reacts on the body that impels it from its natural state."

To act upon each other; to exercise a reciprocal or a reverse effect, as two or more chemical agents; to act in opposition.

To cause chemical agents to react; to cause one chemical agent to react with another.