The sentence does not make sense. Both halves are true,
but when they’re put together the statement makes no
sense. Do not fill in the CE oval.
- F, T Divide and conquer. The first statement is false. Pressure and
volume do have a relationship: PV = nRT.
Now, what about the second statement? It’s true. Look
at the ideal gas law: PV = nRT. Temperature and
volume are on opposite sides of the equation, so they’re
directly proportional when other variables are constant.
The first statement is false, and the second is true.
- D Don’t fall into the temptation trap. In an ideal gas there is no
attraction or repulsion between molecules, so eliminate (A) and (B). Gas
molecules are in continuous motion in both ideal and nonideal gases, so
eliminate (C). In a real gas, molecules will slightly attract each other. As a
result, gas molecules strike the container walls with less force. Less force
means lower pressure. So pressure is less in the real situation as compared
to the ideal. That’s why (D) is correct.
- D This is a partial pressure question. You know that the total pressure
of the system is 1,200 torr, and you know that each gas contributes to the
total pressure by exerting a partial pressure.
There are a total of 24 moles of gases in the container.
The helium concentration is 2 moles/L. We’ve got 4 L
total, so there are 2 × 4 = 8 moles of helium molecules
in the mixture. Hydrogen’s concentration is 1.5
moles/L, so we’ve got 1.5 × 4 = 6 moles of hydrogen
molecules. 8 + 6 = 14. Since the total number of moles
of molecules—for all 3 gases—is 24, there must be 10
moles of carbon dioxide molecules in the mixture.
If there are 10 moles of carbon dioxide molecules and
24 moles of molecules total, carbon dioxide’s mole
fraction = . Total pressure = 1,200 torr, and
