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CHEM 121 > Chapter 5 - Gas Laws > Flashcards

Chapter 5 - Gas Laws Flashcards

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1
Q

What is the equation for pressure?

A

force/area = N/m^2 = Pa

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2
Q

What is Boyle’s Law

A
  • pressure and volume are inversely proportional
  • temperature and number of moles are unchanged
  • k is constant at a specific temperature
  • a plot of V vs. 1/P should be a straight line with slope k and intercept of zero
  • only approximately describes the behavior of gases
  • P x V (at constant T) is not exactly constant for all gases
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3
Q

What is ideal gas?

A
  • a gas that strictly obeys Boyle’s law

ex. an increase in P generates the same PV` value

  • since k is constant: P1V1=k=P2V2
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4
Q

What is Charles’ law?

A
  • volume increases linearly with temperature, at constant pressure for a fixed amount of gas
  • P and # of moles remains constant
  • therefore, if T increase, V also increases
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5
Q

What is the temp at absolute zero?

A
  • 0K or -273.2C
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6
Q

What is the temp at absolute zero?

A

W- 0K or -273.2C

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7
Q

What is Gay-Lussac’s law?

A
  • pressure and temp are directly proportional
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8
Q

What is Avogadro’s law?

A
  • volume is proportional to the # of moles of gas
  • equal volumes of gases at the same temp and pressure contain the same number of particles
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9
Q

WHat is the ideal gas law equation?

A

pv = nrt

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10
Q

What is R

A

the universal gas constant

  • 0.08206 Latm/Kmol
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11
Q

What is this number?:22.42L

A
  • volume of 1 mole of an ideal gas at STP
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12
Q

Review differences in densities of gases and solids/liquids

A
  • gas densities depend strongly on P and T:
    — density increases as P increases: volume decreases
    — density decreases as T increases: volume increases
  • densities of liquids and solids are not affected as much by changes in P and T
  • density of gases are directly proportional to the molar mass
  • no simple relationship exists between the density of solids and liquids and their molar masses
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13
Q

If 200mL of liquid N2 all becomes gas (ex. at room temp, 298K and 1atm), what volume of gas is produced?

If the liquid N2 is sealed in a 2L vessel, what is the interior pressure of the vessel after the liquid becomes gas at 298K?

A

a)
200mL N2(l) - how many L of gas at 298K, 1atm
Find # moles N2 in 200mL liquid
NEED DENSITY! : 0.808g/cm^3 * 1/cm^3/ml = 161.6G N2

Molar mass N2: 28.02g/mol

161.6g N2/ 28.02g/mol = 5.77 moles N2

V = nRT/P = 141L N2

b) pressure of this gas contained in 2L vessel

P = nRT/V = 70.5atm - 70x room pressure - boom!

b) could use P1V1 = P2V2

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14
Q

What is dalton’s law of partial pressures

A
  • in a mixtur eof gases, the total pressure exerted is the sum of the pressures that each gas would exert if it were alone in the container
  • the pressure exerted by each gas in the mixture is referred to as partial pressure

Ptotal = P1 + P2 + p3 + = (ntotalRT)/V

the actual identity of the particles (ex. H2, CO2, He, …) is not important

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15
Q

What is the mole fraction?

A
  • the ratio of the # of moles of a given component in a mixture to the total # of moles in the mixture

X1 = n1/ntotal

since, n= PV/RT, x1 = (P1V/RT)/(PtotalV/RT) = P1/Ptotal

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16
Q

What is the equation for partial pressure

A
  • the partial pressure of any component of a gas mixture is the mole fraction of that component times the total pressure
  • P1 = x1*Ptotal
17
Q

Review important points

A
  • the total # of moles (ntotal) is important in determining Ptotal
  • the volume occupied by individual gas molecules is not important
  • the forces between molecules is not important
  • if the last 2 were important, then Ptotal would depend on the identity of the gas molecules in the mixture
18
Q

What is vapour pressure?

A
  • the pressure that results from a liquid when the rate of evaporation = rate of condensation in a closed container
  • increases with increasing temp
19
Q

a chemist heats KClO3(s) and collects the oxygen that is formed by water displacement in an inverted test tube at 22C. Given that the vapor pressure of water at 22C is 21 torr, calculate the partial pressure of O2 and the mass of KClO3 used if the volume and the total pressure of the gas is 0.650L and 754 torr, respectively.

2KClO3(s) -> 2KCl(s) + 3O2(g)

A

Ptotal = PO2 + PH2O
754 = PO2 + 21
PO2 = 733 torr = 0.964 atm

PO2V = nRT

nO2 = 2.59*10^-2 mole O2

2KClO3(s) gives us 3O2(g)
moles KClO3 = 2.5910^-2 moles O2 * (2mol KClO3)/(3mol O2) = 1.7310^-2 mol KClO3

KClO3 = 122.6 g/mol

therefore, 2.12g of KClO3

20
Q

What is the kinetic molecular theory (KMT) of gases?

A
  • simple model used to explain experimental observations about ideal gas behaviour
21
Q

What are the 4 postulates of KMT?

A
  • due to large inter-particle distances, the volume of individual gas particles is assumed to be negligible
  • the collisions of the particles with the walls of the container give rise to pressure
  • the particles do not exert any force on each other
  • the average kinetic energy of a gas particle is directly proportional to the temperature of the gas (in Kelvin)
22
Q

review summary of concepts behind the kinetic model

A
  • derive an eq for the change in momentum of a particle impinging on one set of parallel walls
  • derive an eq for the force of a particle impinging on one set of parallel walls
  • eq for the total force of a particle impinging on all 6 walls
  • using P=F/A, determine total pressure due to one average particle
  • multiply by nNA for total pressure of n moles of gas
  • replace momentum term for a kinetic energy term
  • this produces an eq for pressure in terms of kinetic energy (energy due to a moving particle)
23
Q

give a summary of the KMT and the individual gas laws

A

Boyle’s law
- V is inversely proportional to P (constant T)
- gases can be compressed: particles are small compared to space between them
- when V decreases the frequency of collisions between particles and wall increases, P increases

Gay Lussac’s Law
- P is proportional to T (constant V)
- if T increases, KE of particles increases = more collisions with fixed walls, pressure increases

Charles Law
- V is proportional to T (Constant P)
- if T increases, KE of particles increases = more collisions with movable walls, volume increases

Avogadro’s Law
- V is proportional to n (constant P)
- more particles, more collisions on movable walls, volume increases

24
Q

What is effusion of gases?

A
  • passage of gas molecules through a small hole into an evacuated chamber
25
Q

What is Graham’s law of effusion?

A
  • the rate of effusion of 2 different gases (same T, P) are inversely proportional to the square roots of their molar masses (M)
  • expect that rate of effusion of gas will depend directly on the average velocity of its particles
26
Q

is diffusion slow or fast

A

slow even though the molecular speeds are fast

  • diffusion rate related to the ratio of distances travelled by gases, which is related to the particle velocity
27
Q

What can we use the ratio of root M2/M1 to compare with?

A
  • molecular speeds
  • rate of effusion
  • effusion times
  • distance traveled by molecules
  • amount of gas effused
28
Q

review summary of ideal behaviour in real gases

A

for a gas at low pressure:
- there are few particles per unit volume
- volume of particle is neglibible compared to volume of the container
- interactions are minimized
- real gas behaves more like ideal gas at low pressure

for a gas at high temperature
- less interaction, particles move further apart, larger volume
- at low temp, volume decreases, particles closer together
- real gas behaves more like an ideal gas at high temp

CHEM 121 (5 decks)

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