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My MCAT Study > General Chemistry- The Gas Phase > Flashcards

General Chemistry- The Gas Phase Flashcards

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MCAT flashcards
1
Q

What are the three different physical forms matter can exist as?

A

Gas
Liquid
Solid

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2
Q

What are the general names for the different physical forms of matter?

A

Phases or states

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3
Q

How are gases classified? Why? Why are they different from liquids?

A

Classified as fluids because they can flow and take on the shapes of their containers. However, the atoms or molecules in a gaseous sample move rapidly and are far apart from each other.

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4
Q

What is weak in gas molecules? What does this result in?

A

Intermolecular forces.
Results in certain characteristic physical properties, such as the ability to expand to fill any volume. Gases are also easily compressible, which distinguishes them from liquids.

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5
Q

How can you define the state of a gaseous sample, what 4 factors?

A

Pressure (P)
Volume (V)
Temperature (T)
Number of moles (n)

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6
Q

What units are used for pressure?

A

1 atm= 760 mmHg= 760 torr= 101.325 kPa

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7
Q

How does a barometer work?

A

Atmospheric pressure creates a downward force on the pool of mercury at the base of the barometer while the mercury in the column exerts an opposing force (its weight) based on its density. The weight of the mercury creates a vacuum in the top of the tube. When the external air exerts a lower force than the weight of the mercury, the column falls.

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8
Q

What units are used for volume of gas?

A

liters (L)

milliliters (mL)

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9
Q

What units is temperature usually expressed in?

A 
Kelvins (K)
Although Celsius (C) may be used
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10
Q

Many processes involving gas take place under which conditions?

A

Standard temperature and pressure (STP) which refers to 273 K (0 degrees celsius)

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11
Q

Is STP conditions the same as standard state conditions?

A

No

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12
Q

When are STP or SSC used?

A

STP (273 K and 1 atm) is generally used for gas law calculations; standard state conditions (298 K, 1 atm, 1 M concentrations) are used when measuring standard enthalpy, entropy, free energy changes, and electrochemical cell voltage.

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13
Q

What is an ideal gas?

A

A hypothetical gas with molecules that have no intermolecular forces and occupy no volume.

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14
Q

How are real gases the same or different from ideal gases?

A

Real gases deviate from this ideal behavior at high pressures (low volumes) and low temperatures, many compressed real gases demonstrate behavior that is close to ideal.

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15
Q

Who discovered the ideal gas law, when?

A

Benoit Paul Emile Clapeyron (1834)

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16
Q

What laws were discovered before the ideal gas law?

A

Boyle’s law, charle’s law, and dalton’s law

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17
Q

What is the ideal gas law equation?

A

PV= nRT

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18
Q

What do the letters represent in the ideal gas law equation?

A 
P: pressure
V: volume
n: Number of moles
T: temperature
R:  The ideal gas constant (8.21X10^-2  L (atm)/mol K) or (8.314 J/K mol)
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19
Q

Will the values for the ideal gas constant be provided on test day?

A

Yes

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20
Q

Why is the ideal gas law used?

A

To determine the missing term when given all of the others. It can also be used to calculate the change in a term while holding two of the others constant. It is most commonly used to solve for volume or pressure at any given temperature and number of moles.

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21
Q

The ideal gas law is also used to determine what?

A

Gas density and molar mass

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22
Q

How do you define density?

A

(p) as the ratio of the mass per unit volume of a substance

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23
Q

What units are usually used for density of a gas?

A

Grams per liter

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24
Q

How many liters is ideal gas at STP?

A

22.4L

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25
Q

When is the combined gas law used?

A

To relate changes in temperature, volume, and pressure of a gas.

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26
Q

What is the combined gas law equation?

A

P1V1/T1 = P2V2/T2

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27
Q

What do the units represent in the combined gas law equation?

A

The subscripts 1 and 2 refer to the two states of the gas (at STP and at the conditions of actual temperature and pressure, for example).

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28
Q

What is assumed stable in the combined gas law?

A

Number of moles

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29
Q

How do you calculate a change in volume using the combined gas law?

A

V2= V1 [P1/P2] [T2/T1]

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30
Q

How do you find the density of gas under nonstandard conditions after finding the volume change in gas?

A

V2 is then used to find the density of the gas under nonstandard conditions.
p= m/V2

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31
Q

How can you predict changes using the combined gas law?

A

Doubling the temperature of a gas would result in doubling its volume, and doubling the pressure of a gas would result in halving the volume, so doubling both the temperature and pressure at the same time results in a final volume that is equal to the original volume.

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32
Q

What is Avogadro’s Principle?

A

All gases at at a constant temperature and pressure occupy volumes that are directly proportional to the number of moles of gas present. Equal amounts of all gases at the same temperature and pressure will occupy equal volumes

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33
Q

One mole of any gas will occupy how many liters?

A

22.4 liters at STP

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34
Q

What equations are associated with avogadro’s principle?

A 
n/V= k 
n1/V1 = n2/V2
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35
Q

What do the letters represent in the equation associated with avogadro’s principle?

A

k: constant
n1 and n2: number of moles of gas 1 and gas 2
V1 and V2: Volumes of the gases

36
Q

How can Avogardro’s principle equation be summarized?

A

The number of moles of gas increases, the volume increases in direct proportion.

37
Q

What is Boyle’s Law?

A

For a given gaseous sample held at constant temperature (isothermal conditions) the volume of the gas is inversely proportional to its pressure:
PV = k
P1V1 = P2V2

38
Q

What do the letters represent in Boyle’s Law?

A

k: a constant

Subscripts 1 and 2 represent two different sets of pressure and volume conditions

39
Q

Simplified, what is Boyle’s Law?

A

Ideal gas law with n and T constant

40
Q

What does Charle’s Law state?

A

At constant pressure, the volume of a gas is proportional to its absolute temperature, expressed in Kelvins.
V/T= k
V1/T1 = V2/T2

41
Q

Simplified, Charles Law is what?

A

Ideal gas law when n and p are constant

42
Q

According to Boyle’s Law as pressure increases ______ decrease.

A

Volume

43
Q

According to Charles’s Law, as temperature increases, __________ increases.

A

Volume

44
Q

What is Gay-Lussac’s Law?

A 
P/T= k 
P1/T1 = P2/T2
45
Q

How is Gay-Lussac’s Law simplified?

A

Ideal gas law with n and V constant

46
Q

In Gay-Lussac’s Law, as Temperature increase, _______ increases.

A

Pressure

47
Q

When two or more gases that do not chemically interact are in the same vessel, what happens?

A

Each gas will behave independently of the others. That is, each gas will behave as if it were the only gas in the container. The pressure exerted by each gas in the mixture will be equal to the pressure that the gas would exert if it were the only gas in the container.

48
Q

What is partial pressure?

A

The pressure exerted by each individual gas

49
Q

What is Dalton’s Law of partial pressures?

A

The total pressure of a gaseous mixture is equal to the sum of the partial pressure of the individual components.
(PTotal)= (Pa) + (Pb) + …

50
Q

How can the partial pressure of a gas be determined with what equation?

A

Partial pressure is related to the mole fraction.
Pa= Xa Pt
Where Xa = moles of gas A/ total moles of gas

51
Q

What is Henry’s Law?

A

At various applied pressures, the concentration of a gas in a liquid increased or decreased. This was a characteristic of a gas’s vapor pressure.

52
Q

What is vapor pressure?

A

The pressure exerted by evaporated particles above the surface of a liquid.

53
Q

What equation is used to measure the vapor pressure using Henry’s Law?

A 
[A]= kH x Pa 
[A]1/P1 = [A]2/P2 = kH
54
Q

What do the letters represent in the equation for Henry’s Law?

A

kH: Henry’s Constant (The value depends on the identity of the gas)
Pa: Partial pressure of A

55
Q

According to Henry’s Law, What are related?

A

Solubility (concentration) and pressure are related

56
Q

If the atmospheric pressure changes, what happens to the partial pressure and the amount of gas exchange?

A

The partial pressure of oxygen in the atmosphere also changes and the amount of gas exchanged is altered accordingly; if the partial pressure of a particular gas is elevated, such as when giving hyperbaric oxygen, the amount of that gas dissolved in the blood is also elevated.

57
Q

What is the kinetic molecular theory used for?

A

Explain the behavior of gases, which the other laws merely described.

58
Q

What do the gas laws demonstrate?

A

All gases show similar physical characteristics and behavior irrespective of their particular chemical identity.

59
Q

What are the assumptions for kinetic molecular theory?

A
  1. Gases are made up of particles with volumes that are negligible compared to the container volume
  2. Gas atoms or molecules exhibit no intermolecular attractions or repulsions.
  3. Gas particles are in continuous, random motion, undergoing collisions with other particles and container walls.
  4. Collisions between any two gas particles (or between particles and the container walls) are elastic, meaning that there is conservation of both momentum and kinetic energy
  5. The average kinetic energy of gas particles is proportional to the absolute temperature of the gas (in kelvins) and it is the same for all gases at a given temperature, irrespective of cheical identity or atomic mass.
60
Q

What is the average kinetic energy of a gas particle equation?

A

KE= 1/2mv^2 = 3/2 kb T

61
Q

According to the kinetic molecular theory, the average KE is proportional to what?

A

Absolute temperature of the gas

62
Q

What is kb according to the kinetic molecular theory?

A 
Boltzmann constant (1.38 x 10^-23 J/K)
Which serves as a bridge between the macroscopic and microscopic behaviors of gases
63
Q

How are the speeds of gases defined?

A

In terms of their average molecular speed

64
Q

How do you define an average speed of a molecule?

A

Determine the average kinetic energy per particle and then calculate the speed to which this corresponds.

65
Q

What is another name for the average speed of a molecule?

A

root-mean-square speed (u rms)

66
Q

What equation is used to find the root-mean-square speed?

A

u rms= Square root 3RT/M

67
Q

What do the letters represent in the root-mean-square speed equation?

A

R: ideal gas constant
T: temperature
M: molar mass

68
Q

What does Maxwell-Boltzmann distribution curve show?

A

The distribution of gas particle speeds at a given temperature.

69
Q

What happens to the Maxwell-Boltzmann curve as the temperature increase? What does it mean?

A

It flattens and shifts to the right when temp increase.

Indicating that at higher temps, more molecules are moving at higher speeds.

70
Q

What is diffusion?

A

The movement of molecules from high concentration to low concentration through a medium (such as air or water)

71
Q

What does the kinetic molecular theory of gases predict?

A

Heavier gases diffuse more slowly than lighter ones because of their differing average speeds.

72
Q

What must be true, if all gas particles have the same average kinetic energy at the same temperature?

A

Particles with greater mass travel at a slower average speed.

73
Q

What is Grahm’s Law?

A

Under isothermal and isobaric conditions, the rates at which two gases diffuse are inversely proprtional to the square roots of their molar masses.

74
Q

What is the equation for Graham’s Law?

A

r1/r2 = Square root M2/M1

75
Q

What do the letters represent in Graham’s Law equation?

A

r1 and r2: diffusion rates of gas 1 and 2

M1 and M2: Molar masses of gas 1 and 2

76
Q

What can be determined from Graham’s Law?

A

A gas that has a molar mass four times that of another gas will travel half as fast as the lighter gas.

77
Q

What is Effusion?

A

The flow of gas particles under pressure from one compartment to another through a small opening

78
Q

Graham used the kinetic molecular theory to show what about Effusion?

A

For two gases at the same temperature, the rates of effusion are proprional to the average speeds. The rates of effusion can be looked at in terms of molar mass. The relationship is the same for diffusion.

79
Q

All real gases deviate from what?

A

Ideal gas behavior, particularly when the gas atoms or molecules are forced into close proximity under high pressure

80
Q

At moderately high pressures what deviation in real gases can be seen compared to the ideal gas?

A

A gas’s volume is less than would be predicted by the ideal gas law due to intermolecular attraction.

81
Q

At extremely high pressures, what deviation in real gases can be seen compared to predicted ideal gas?

A

The size of the particles becomes relatively large compared to the distance between them, and this causes the gas to take up a larger volume than would be predicted. The ideal gas law assumes that a gas can be compressed to take up zero volume, this is not actually possible

82
Q

As the temperature of a gas is reduced, what deviation in real gases can be seen compared to the predicted ideal gas?

A

Intermolecular attraction causes the gas to have a smaller volume than that would be predicted

83
Q

The closer a gas gets to its boiling point, how does it compare to the predicted ideal gas?

A

The less ideally it acts

84
Q

At extremely low temperatures, what deviation can be seen compared to the predicted ideal gas?

A

Gases will again occupy more space than predicted

85
Q

What is the Van Der Waals equation?

A

(P + (n^2)a /V^2) (V - nb) = nRT

86
Q

What do the letters represent in the Van Der Waal equation?

A

a and b: physical constants experiementally determined for each gas (a corrects for the attractive forces between molecules and b corrects for the volume of the molecules themselves.)

87
Q

What are mneumonics for the letters in the Van Der Waals equation?

A

“a” is attractive forces

“b” is big particles

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