Return to MCAT® Blog Homepage

MCAT Chemistry Question — Hypothetical Reaction

The Keq for the following hypothetical reaction is 5.16 x 10-6.

A2B (g) + C2 (g) → ABC (s) + AC (g)

Which of the following is true concerning this reaction?


A) The Keq value indicates that reactants are highly favored.

B) The Keq value indicates that products are highly favored.

C) The formation of a solid indicates a increase in ΔS.

D) The formation of a solid indicates a negative value for ΔG.



The Keq equation for the above reaction is:

Keq = [AC] / [A2B][C2]

Remember that solids and liquids do not appear in Keq equations. Since the value of Keq is given as 10-6, we can conclude that the reaction vastly favors the reactants in the denominator. Thus (A) is the correct answer.

B: This would be true if the Keq were much more than 1, rather than less than 1 as given in the question.

C: Going from gas to solid indicates a decrease in ΔS.

D: The phase changes present in a reaction do not determine the ΔG. They have an effect, but are not the sole factor. You must also account for ΔH.

Want more MCAT practice?

We’ve got options for every schedule and learning style!

From the best online MCAT course created by top instructors with 524+ MCAT scores to the most representative full-length practice exams and private tutoring, we can custom tailor your MCAT prep to your goals!

Not sure which option is right for you? Schedule a free MCAT consultation with an MCAT expert using the form below. No obligation, just expert advice.

Create your Free Account to access our MCAT Flashcards SIGN UP NOW
MCAT is a registered trademark of the Association of American Medical Colleges (AAMC), which is not affiliated with Blueprint.