A change in conditions that upsets the balance of forward and reverse rates is called a:

1. At equilibrium the forward and reverse reaction rates are equal. 2. If an equilibrium system is subjected to a change in conditions that affects these reaction rates differently, that change is a stress. 3. Then the rates are no longer equal and the system is not at equilibrium. 4. A catalyst speeds both directions equally, so it does not shift the position. _Source: OpenStax Chemistry 2e (CC BY 4.0), Ch 13 'Fundamental Equilibrium Concepts', sections 13.1-13.4_