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CHEM1601 > Chapter 10: Gases > Flashcards

Chapter 10: Gases Flashcards

1
Q

Define pressure.

A

Pressure is the force exerted per unit area by gas particles as they strike the surfaces around them.

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2
Q

What are the three basic assumptions of the kinetic molecular theory of gases?

A
  1. The size of a particle is negligibly small.
  2. The average kinetic energy of a particle is proportional to the temperature in kelvins.
  3. The collision of one particle with another (or with the walls of its container) is completely elastic.
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3
Q

How is kinetic energy related to temperature? What about velocity?

A

Kinetic energy is proportional to temperature. However, velocity is not proportional. Atoms that are lighter must move faster (have greater velocity) to have the same kinetic energy as heavier atoms.

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4
Q

What does it mean to say that the collisions between particles are completely elastic in the kinetic molecular theory of gases?

A

This means that when two particles collide, they may exchange energy, but there is no overall loss of energy. Between collisions, the particles do not deform and they do not exert any forces on one another.

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5
Q

How does the number of gas particles in a given volume affect force and pressure?

A

The fewer the gas particles, the lower the force per unit area and the lower the pressure.

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6
Q

How is pressure related to altitude and why?

A

Because the number of gas particles in a given volume generally decreases with increasing altitude, pressure decreases with increasing altitude.

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7
Q

How does a barometer work?

A

A barometer is an evacuated glass tube, the tip of which is submerged in a pool of mercury. Atmospheric pressure on the liquid mercury’s surface forces the mercury upward into the evacuated tube. When the atmospheric pressure rises, the height of the mercury column rises as well.

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8
Q

What is the SI unit of pressure, and what is it defined as?

A

The SI unit of pressure is the pascal (Pa), defined as 1 newton per square meter.

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9
Q

Define manometer.

A

A manometer is a U-shaped tube containing a dense liquid, usually mercury. It is used to measure the pressure exerted by a sample of gas.

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10
Q

What is Boyle’s law?

A

There is an inverse relationship between the pressure of a gas and its volume for constant temperature and amount of gas.

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11
Q

What is Charles’s law?

A

For constant pressure, the volume of a gas increases with increasing temperature. V and T are linearly related.

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12
Q

Why must calculations for Charles’s law always be done using kelvins?

A

The volume of a gas is directly proportional to its absolute temperature, not its temperature in ˚C.

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13
Q

What is Avogadro’s law?

A

The volume of a gas sample increases linearly with the number of moles of gas in the sample at constant temperature and pressure.

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14
Q

What is the ideal gas law?

A

The ideal gas law combines the relationships between pressure, volume, temperature, and moles established by Boyle’s, Charles’s, and Avogadro’s laws.

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15
Q

What is Gay-Lussac’s law?

A

As the temperature of a fixed amount of gas in a fixed volume increases, the pressure increases.

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16
Q

How is the pressure on the wall of a container occupied by particles in constant motion calculated?

A

The pressure is the total force on the wall (due to the collisions) divided by the area of the wall.

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17
Q

Define molar volume.

A

Molar volume is the volume occupied by one mole of a substance.

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18
Q

What is standard temperature and pressure for gases?

A

Standard temperature is 0˚C or 273 K and pressure is 1.00 atm.

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19
Q

What is the molar volume of an ideal gas at STP?

A

22.4 L

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20
Q

What is the relationship between the density of a gas and its molar mass?

A

The density of a gas is directly proportional to its molar mass. The greater the molar mass of a gas, the more dense the gas. This explains why gases with a molar mass less than that of air tends to rise in air.

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21
Q

Define partial pressure.

A

Partial pressure is the pressure due to any individual component in a gas mixture.

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22
Q

What is Dalton’s law of partial pressures?

A

Adding different kinds of gases to a gas mixture has the same effect on pressure as simply adding more particles. The partial pressures of all the components sum to the overall pressure.

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23
Q

What is the mole fraction?

A

The mole fraction is the number of moles of a component in a mixture divided by the total number of moles in the mixture. For gases, the mole fraction of a component is equivalent to its percent by volume divided by 100%.

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24
Q

What is the relationship between vapor pressure and temperature?

A

Vapor pressure (pressure of water in a mixture) increases with increasing temperature because higher temperatures cause more water molecules to evaporate.

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25
Q

Do heavy or light particles in a gas travel faster on average?

A

In a gas mixture at a given temperature, lighter particles travel faster than heavier ones.

26
Q

What is mercury’s phase at standard conditions?

A

Liquid.

27
Q

What is bromine’s phase at standard conditions?

A

Liquid.

28
Q

What is iodine’s phase at standard conditions?

A

Solid.

29
Q

Which elements have a standard state that is a dimeric form?

A

H2, N2, O2, F2, Cl2, Br2, and I2.

30
Q

In barometric pressure problems, what does it mean when the gas pushes against the atmosphere?

A

It means the pressure of the gas is greater than the atmospheric pressure. This also means the pressure of the gas and the atmospheric pressure must be added together to find the total pressure.

31
Q

What is the difference between temperature at standard conditions and at STP?

A

At STP, temperature is 0˚C. At standard conditions, temperature is 25˚C.

32
Q

How is pressure indicative of the weather?

A

High pressure (P>749 mmHg) indicates a clear day. Low pressure (P<741 mmHg) indicates a rainy/stormy day. Lowest atmospheric pressures are associated with our most intense weather phenomena: tropical cyclones.

33
Q

What does a manometer measure, and how does it do so?

A

The pressure of a sealed gas. The manometer measures the pressure differential between the sealed gas and atmosphere using a u-shaped tube filled with Hg. The higher pressure system will push the Hg further along the tube, causing a height difference. A complementary barometer is required for this process.

34
Q

Which of the gas laws led to the creation of absolute zero? How was this done?

A

The relationship described by Charles’s law allows us to extrapolate the temperature at which a gas has “zero volume.” Anything lower than this would imply negative volume (which is impossible). This inspired Lord Kelvin to create an absolute temperature scale that bears his name.

35
Q

All of the simple gas laws show an interconnectedness between which four different variables?

A

Volume, temperature, pressure, and # of gas particles.

36
Q

Define partial pressure.

A

The pressure due to any individual component in a gas mixture.

37
Q

What is Dalton’s law of partial pressures?

A

The sum of the partial pressures of a gas mixture is the total pressure.

38
Q

Define mole fraction.

A

The number of moles of a component in a mixture divided by the total number of moles in the mixture is the mole fraction.

39
Q

How is partial pressure related to mole fraction?

A

The partial pressure of a component in a gaseous mixture is its mole fraction multiplied by the total pressure.

40
Q

What is the relationship between vapor pressure and temperature?

A

Vapor pressure increases with increasing temperature because higher temperatures cause more water molecules to evaporate.

41
Q

Define mean free path.

A

The average distance that a molecule travels between collisions.

42
Q

How is mean free path related to pressure?

A

Mean free path increases with decreasing pressure.

43
Q

Define diffusion.

A

Diffusion is the process by which gas molecules spread out in response to a concentration gradient.

44
Q

Define effusion.

A

The process by which a gas escapes from a container into a vacuum through a small hole.

45
Q

How is the rate of effusion related to the molar mass of the gas?

A

The rate of effusion–the amount of gas that effuses in a given time–is inversely proportional to the square root of the molar mass of the gas.

46
Q

Under STP, one mole of an ideal gas occupies what volume?

A

22.4 L

47
Q

What two criteria must be met for a gas to act ideally?

A
  1. The volume of the gas particles is small compared to the space between them.
  2. The forces between the gas particles are not significant.
    At STP, these assumptions are valid for most common gases. However, these assumptions break down at higher pressures or lower temperatures.
48
Q

What is the effect of intermolecular attractions between gas particles at low temperatures?

A

There is a decrease in the number of collisions with the surfaces of the container, and a corresponding decrease in the pressure compared to that of an ideal gas.

49
Q

What is the van der Waals equation used to calculate?

A

The properties of a gas under nonideal conditions.

50
Q

How are the mole fraction, partial pressure, and total pressure related?

A

The partial pressure of one gas is equal to the mole fraction times the total pressure.

51
Q

What are the two assumptions about gases made by kinetic molecular theory?

A
  1. Gas particles are in constant motion.
  2. The attractive forces between gas molecules are negligible.
52
Q

What are the three postulates of kinetic molecular theory?

A
  1. In comparison to the size of their container, the size of gas particles are negligibly small.
  2. The average kinetic energy of a gas particle is proportional to temperature in Kelvins. (KEavg = 3/2RT)
  3. The collisions experienced by gas particles are completely elastic.
53
Q

Why do gases in the same container have the same average kinetic energy?

A

Gases in the same container have the same temperature, thus they have the same average kinetic energy.

54
Q

To have the same temperature, gas particles with differing masses must also have different what?

A

Different average velocities.

55
Q

Why do we use root mean square velocity instead of regular velocity?

A

Velocity is a vector, meaning it has both magnitude and direction. To avoid the problem of certain particles’ velocities canceling each other out, root mean square velocity is used because it is directionless.

56
Q

How does the rms velocity compare to the average molecular velocity?

A

They are close in value but not equal. rms velocity > average velocity.

57
Q

What are the units of the R value?

A

8.314 J/(mol x K)

58
Q

What is the relationship between the rate of movement during diffusion and effusion and its molar mass?

A

For gases at the same temperature, the rate of movement is inversely proportional to the square root of its molar mass.

59
Q

Why does kinetic molecular theory fail at high pressure?

A

Gas particles have a finite volume, therefore, if more particles are compressed into a smaller volume (resulting in increased pressure), the volume of the gas particles is no longer negligible.

60
Q

Is the molar volume of gases at high pressure higher or lower than predicted by the ideal gas law?

A

Higher.

61
Q

Is the observed pressure of a real gas at relatively low temperatures higher or lower than predicted by the ideal gas law?

A

Lower.

CHEM1601 (17 decks)

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