What will most likely happen when stress is applied to an equilibrium reaction? the system will not respond to the stress. the system will use catalysts to change its equilibrium. the equilibrium position will shift to increase the applied stress. the system will change its concentration to shift to a new equilibrium position.

The system will change its concentration to shift to a new equilibrium position.

Explanation:

For example  in the Haber Process

N2  +  3H2  ⇄  2NH3

If the pressure is increased the  process will move to the right - to have more NH3 and less of the nitrogen and hydrogen.

The system will change its concentration to shift to a new equilibrium position.

Explanation:

According to Le Chatelier’s principle when a stress is applied to a system, the equilibrium shifts to counteract the applied stress, such that a new equilibrium position is formed.  

For example, ice and water is taken in a closed container. Let the temperature of the closed container be raised. The equilibrium of the system will shift to the product side, it will use up the added energy and more water will be formed from the ice.  

ice + energy --> water