States and Phases of Matter

Sample questions

Showing 10 of 70 questions from this chapter. The full bank is in the chapter test below.

1. 1

   A gas can be compressed easily into a much smaller volume because:

   • A.✓ most of the volume of a gas is empty space between its molecules (correct answer)
   • B.the molecules of a gas are held together by strong attractive forces
   • C.the molecules of a gas are closely packed as in a solid
   • D.each molecule of a gas has a large volume of its own

   Why: Gas molecules are widely separated and about 99.9 percent of the volume of a gas is empty space, so the gas can be squeezed into a much smaller volume. Strong attractive forces or close packing would oppose compression, and gas molecules have negligible volume of their own.
2. 2

   The cooling that takes place when a gas expands suddenly is known as:

   • A.Hess effect
   • B.Seebeck effect
   • C.✓ Joule-Thomson effect (correct answer)
   • D.Tyndall effect

   Why: The Joule-Thomson effect is the fall in temperature that accompanies the sudden expansion of a gas. Hess, Seebeck and Tyndall effects belong to thermochemistry, thermoelectricity and light scattering respectively.
3. 3

   The pressure exerted by a gas on the walls of its container is caused by:

   • A.the weight of the gas molecules pulling downwards
   • B.✓ collisions of gas molecules with the walls of the container (correct answer)
   • C.attraction between the gas molecules and the container walls
   • D.vibration of the walls of the container

   Why: Gas pressure arises from the bombardment of the container walls by rapidly moving gas molecules. The weight of the gas and any attraction to the walls are far too small to account for the observed pressure.
4. 4

   Which statement is true for an ideal gas?

   • A.Its molecules have a definite volume of their own
   • B.Its molecules attract one another with strong forces
   • C.Its molecules are packed as closely as those of a solid
   • D.✓ The volume of its molecules themselves is taken as zero (correct answer)

   Why: An ideal gas is assumed to have zero particle volume and negligible intermolecular forces, so the whole container volume is treated as free space. Real gas molecules have a small volume and do exert weak attractive forces on one another.
5. 5

   The value of the ideal gas constant R, when pressure is in atm and volume in $\pu{dm3}$, is:

   • A.8.314 $\pu{atm dm3}$ $\pu{K-1}$ $\pu{mol-1}$
   • B.✓ 0.0821 $\pu{atm dm3}$ $\pu{K-1}$ $\pu{mol-1}$ (correct answer)
   • C.62.4 $\pu{atm dm3}$ $\pu{K-1}$ $\pu{mol-1}$
   • D.1.987 $\pu{atm dm3}$ $\pu{K-1}$ $\pu{mol-1}$

   Why: R equals 0.0821 $\pu{atm dm3}$ $\pu{K-1}$ $\pu{mol-1}$ when pressure and volume are expressed in atm and $\pu{dm3}$. The value 8.314 belongs to the SI form of the constant, in $\pu{J K-1}$ $\pu{mol-1}$.
6. 6

   Which of the following is the ideal gas equation?

   • A.PV = nR/T
   • B.PVT = nR
   • C.P = nRTV
   • D.✓ PV = nRT (correct answer)

   Why: Combining Boyle's, Charles's and Avogadro's laws gives V = nRT/P, which on rearrangement becomes PV = nRT. The other expressions do not reduce correctly when the three gas laws are applied.
7. 7

   For a fixed amount of gas at constant temperature, the volume is inversely proportional to the pressure. This statement is:

   • A.✓ Boyle's law (correct answer)
   • B.Charles's law
   • C.Avogadro's law
   • D.Graham's law

   Why: Boyle's law states that V is inversely proportional to P when n and T are held constant. Charles's law relates volume to absolute temperature and Avogadro's law relates volume to the number of moles.
8. 8

   At constant pressure, the volume of a fixed mass of a gas is directly proportional to its absolute temperature. This is:

   • A.Boyle's law
   • B.Avogadro's law
   • C.✓ Charles's law (correct answer)
   • D.Dalton's law

   Why: Charles's law gives V proportional to T when n and P are constant. Boyle's law instead holds the temperature constant and links volume with pressure.
9. 9

   At constant temperature and pressure, the volume of a gas is directly proportional to the number of moles present. This relationship is:

   • A.Boyle's law
   • B.Charles's law
   • C.✓ Avogadro's law (correct answer)
   • D.Graham's law

   Why: Avogadro's law states V proportional to n at constant P and T. Boyle's and Charles's laws deal with pressure and temperature changes at constant amount of gas.
10. 10

    A 134 g sample of a gas occupies 5 $\pu{dm3}$ at 10 atm pressure and 200 K. The relative molecular mass of the gas is: (R = 0.0821 $\pu{atm dm3}$ $\pu{K-1}$ $\pu{mol-1}$)

    • A.✓ 44 g/mol (correct answer)
    • B.22 g/mol
    • C.88 g/mol
    • D.134 g/mol

    Why: M = mRT/PV = (134 x 0.0821 x 200) / (10 x 5) = 2200.3 / 50 = 44 g/mol. Using 200 K instead of the Celsius temperature is essential; substituting -73 directly gives a negative result.