MCAT Chemistry Question — Negative Slope
- Apr 15, 2017
- MCAT Question of the Day
Which of the following best accounts for the negative slope of the liquid-solid equilibrium line in the phase diagram for water?
- H2O(s) has a greater density than H2O(l), which causes the solid to form liquid under high pressure conditions.
- H2O(s) has a greater density than H2O(l), which results from the hydrogen bonds formed between water molecules.
- H2O(s) has a lower density than H2O(l) which results from the crystalline framework that forms due to hydrogen bonds.
- H2O(s) has a lower density than H2O(l) which causes the solid to form liquid under low pressure conditions.
Click for Explanation
This question asks the examinee to identify the correct explanation for the negatively sloped phase diagram for water. During the crystallization of water, each molecule forms four hydrogen bonds with adjacent water molecules resulting in three-dimensional hexagonal lattice structure. Thus, the density of solid water is less than the density of liquid water eliminating choices A and B.
The negatively sloped liquid-solid equilibrium line in the phase diagram means that an increase in pressure at a constant temperature can cause water to change phases from solid to liquid. The increase in pressure causes water to convert to the more compact liquid phase in order to relieve the increased pressure. Therefore, answer choice C is the best answer.
Want more MCAT practice?
Sign up to receive our MCAT of the Day emails!
You’ll get an MCAT-style question to your inbox every weekday. Looking for full-length practice? You can also sign up for our Free MCAT Practice Bundle, which includes a free full-length exam and more!
Search the Blog
Interested in our Online MCAT Course, One-on-One MCAT Tutoring or Med admissions packages? Set up a free consultation with one of our experienced Senior Student Advisors.Schedule Now
MCAT Blog What's on the MCAT?
MCAT Blog How to Review MCAT Full Lengths
Free MCAT Practice AccountNeed great MCAT practice?
Get the most representative MCAT practice possible when you sign up for our free MCAT Account, which includes a half-length diagnostic exam and one of our full-length MCAT practice exams.Learn More