Kaplan MCAT General Chemistry Review

Plugging in 2.7 for e, we can calculate 2.7 ⁽²⁾ = K_eq. Because 2² is 4 and 3² is 9, we can assume that we want an answer choice somewhere in between, which eliminates (A) and (D). Let’s use some logic to choose between (B) and (C). Obviously, 8.9 is very close to 9, so we can assume that its square root is very, very close to 3 (it’s actually around 2.984). The answer choice should be a bit smaller, so (B), 7.4, is correct.

8. D

There is not enough information available to determine the energy of this reaction. Only its entropy is obvious.

9. A

This problem asks you to calculate the free energy of reaction at nonstandard conditions, which you can do using the equation G = G° + RT ln(Q). (R is the gas constant, 8.314 Jmol^-1K^-1).

10. C

There is not enough information to deduce anything about reaction temperature, which eliminates (B) and (D). Adiabatic and isothermal processes are necessarily opposite because adiabatic processes do not involve heat transfers. A reaction at constant pressure can be either adiabatic (no heat transfer to change volume) or isobaric (constant pressure, as the word roots imply).

11. A

This question requires interpreting the equation G = H - . Endergonic (C) indicates a nonspontaneous reaction, and an exergonic reaction (D) indicates a spontaneous reaction. In contrast, endothermic and exothermic reactions suggest the sign of the enthalpy of the reaction. The problem does not provide enough information to determine the free energy of this temperature-dependent reaction. (A) is the correct answer.

12. A

Disorder in the vessel increases over the course of the reaction, so (A) is correct. While we cannot make a quantitative determination of entropy from the picture, we can estimate the relative amount of disorder from the beginning to the end of the reaction in the vessel.

13. C

For a process to occur spontaneously, Q must be less than K_eq and will therefore have a tendency to move in the direction toward equilibrium. A spontaneous reaction’s free energy is negative by convention. (C) is the correct answer. (A), (B), and (D) are opposites.

14. B

A calorimeter measures specific heat or heat capacity. Though calorimeters often incorporate thermometers, the thermometer itself only tracks heat transfers, not the specific heat value itself, so (A) is incorrect. (C) is irrelevant; barometers measure changes in pressure. (D) is also incorrect, as volumetric flasks measure liquid quantities, not the heat capacity of the liquid.

15. C

Memorize the laws of thermodynamics prior to Test Day; they may be stated in several different forms. You should know the equation and how to rephrase it into a sentence or two. The first law often confuses students—keep in mind that it refers to the overall energy of the universe, not to the enthalpy of the universe, even though enthalpy is usually substituted for this term in introductory college chemistry experiments. The third law (absolute zero) is not an equation, so keep that in mind as you work.

16. A

Eliminate (C) and (D), which describe the free energy of reaction and cannot be determined from this graph. If the heat of formation of the products is greater than that of the reactants, the reaction is endothermic. We can determine this information by their relative magnitude on the graph. An exothermic graph would reflect products with a lower enthalpy than that of the reactants.

Chapter 7: The Gas Phase

We are literally surrounded by gas. We walk through it, run through it, breathe it in, breathe it out, burp it, pass it, and if it weren’t for the fact that we are denser than air, we’d be swimming in it. Gases behave in ways that we find useful, interesting, and entertaining. How else to explain the almost universal human delight in balloons: helium balloons, hot air balloons, circus balloon animals, 99 Luftballons? The topic of discussion for this chapter is not, alas, the art of fashioning balloon animals or the deeper meaning of the Cold War–era German protest song. We will discuss the MCAT favorites—the gas phase and the ideal gas laws. We will begin our discussion of ideal gases and the kinetic molecular theory that describes them. We will then examine each of the laws that govern the behavior of ideal gases and conclude with an evaluation of the ways in which the behavior of real gases deviate from that predicted by the ideal gas law.

Before we get started with our discussion of gases, here’s a fun little experiment that you can try on your own, not only to get you thinking about the characteristics of gases but also to help you connect gas behaviors to some of the principles of Newtonian physics that you must know and understand for Test Day. (The MCAT will be making these kinds of connections, so you should be preparing for that now.)