Cracking the SAT Chemistry Subject Test

CHAPTER 8 PHASES: GASES, LIQUIDS, AND

SOLIDS

Drill 1

1. C Remember that values that are on the same side of the ideal gas
   equation are inversely proportional. In PV = nRT, both R and T (Kelvin
   temperature) are on the same side as n (moles of gas). Since R (ideal gas
   constant) cannot change with a change in moles, the answer must be (C).


2. D In a mixture of gases, each fills the container, so (E) cannot be
   right. It doesn’t make sense to add the gases’ temperatures to get a total
   temperature, so (B) and (C) are eliminated. That leaves us with (A) and (D).
   The ideal gas constant is not something that could be summed up for each
   gas either, so the answer is (D). Remember that adding the partial pressures
   of a mixture gives you the total pressure of the system.


3. C Don’t forget that temperature is a measure of average kinetic energy
   and that for ideal gases, Kelvin temperature increases in proportion to
   changes in kinetic energy. (C) is correct.


4. T, T It’s time to divide and conquer. What do you think of the first
   statement by itself? It’s true; it describes kinetic molecular theory.
   The second statement is also true; you know this from
   the ideal gas law: PV = nRT. Temperature and moles of
   gas are on the same side of the equation, so they’re
   inversely proportional when other variables are
   constant.
   Let’s see if the whole sentence makes sense. “If an ideal
   gas is located in a closed container and temperature is
   increased, the average speed of the molecules will
   always increase as well because for an ideal gas,
   temperature and moles of gas are inversely
   proportional.