The equilibrium for the indicator methyl orange is HC14H14SO3(red) + H2O C14H14SO3−(yellow) + H3O+ The reaction is exothermic.

Explain in words, what happens when this is added to an acidic solution.

The solution will turn red.  

Explanation:

HC₁₄H₁₄SO₃ + H₂O ⇌ HC₁₄H₁₄SO₃⁻ +H₃O⁺

     (red)                           (yellow)

Methyl orange is a weak acid in which the ionized and unionized forms are distinct colours and are in equilibrium with each other,

At about pH 3.4,  the two the forms are present in equal amounts, and the indicator colour is orange.

If you add more acid, you are disturbing the equilibrium.

According to Le Châtelier's Principle, when you apply a stress to a system at equilibrium, it will respond in such a way as to relieve the stress.

The system will try to get rid of the added acid, so the position of equilibrium will move to the left.

More of the unionized molecules will form, so the solution will turn red.

the product of the pressure and volume is also constant