Equilibrium Chemistry problem

Question

Consider the following equilibrium reaction in a closed gas container with a constant volume: (= is the arrow that goes both ways) H2(g)+I2(g)=2HI(g) At some point, an amount of deuterium gas (D2) is added to the gasholder. Deuterium (D) is an isotope of hydrogen (H). Which statement is correct?

A. The equilibrium shifts to the right because of the pressure increase in the gasholder.

B. There is no shift of the equilibrium.

C. The balance shifts to the left.

D. None of the previous statements are correct.

The answer is D, please explain to me why, A, B, and C are wrong.

Answer 1

A) is incorrect because you have 2 moles of gas on the reactant side and 2 moles of gas on the product side. Adding D2 increases the pressure and since you have equal moles of gas on both side of the reaction, any change in equilibrium WILL NOT be the result of an increase in pressure in the gasholder

B) is incorrect because D2 acts just like H2 and so adding this should shift the equilibrium to the product (right) side of the reaction

C) is incorrect because if D2 acts like H2, it will shift the equilibrium to the product (right) side, not the left

D) is correct because the equilibrium should shift to the right as explained above.