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General Chemistry 1 > The Gaseous state > Flashcards

The Gaseous state Flashcards

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1
Q

Gases

A
  • made of widely seperated particles in constant motion
  • flow readily and occupy the entire volume of their containers regardless of its shape.
  • can be compressed
  • gas mixtures are always homogeneous.
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2
Q

Gas Pressure

A
  • Force exerted per unit area of surface
  • Pressure results from collision of gas molecules with the walls of their container
  • Force = mass x acceleration
  • acceleration = change in speed per unit time. (m/s2)
  • Newton = (kg • m) / s2
  • Pascal = kg/(m • s2)
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3
Q

Barometer

A
  • Device for measuring the pressure of the atmosphere
  • Measures the pressure of the gases in the atmosphere
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4
Q

Manometer

A

device that measures the pressure of a gas or liquid in a vessel.

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5
Q

What is a torr?

A
  • Millimeter of mercury (mmHg)
  • named after Evangelista Torricelli (1608 - 1647) who invented the mercury barometer in 1643
  • Unit of pressure equal to that exerted bu a column of mercury 1 mm high at 0.00 ºC
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6
Q

Atmosphere (atm)

A
  • is the pressure exerted by a column of mercury exactly 760 mm high at a temperature of 0.00ºC
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7
Q

Empirical Gas Laws

A
  • The physical properties of any gas can be defined by four variables
    • Pressure (P)
    • Temperature (T)
    • Volume (V)
    • and the amount or number of moles (n)
  • These variables are related through simple gas laws that show how one of the variables changes while the other two remain constant.
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8
Q

Boyle’s Law

A
  • Pressure-volume relationship
  • gases can be compressed
  • at constant temperature, the volume of a fixed mass of gas is inversly proportional to the pressure
  • The volume of an ideal gas varies inversly with pressure
  • Gas behavior may deviate from Boyles law at high pressure.
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9
Q

Charles’s Law

A
  • Temperature - volume relationship
  • at constant pressure, the volume of a fixed mass of any gas is directly proportional to the absolute temperature
  • Temperature and volume are directly proportional
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10
Q

Combined gas law

A
  • Boyle and Charles laws can be combined
    • Both T and P cause an increase in V
    • Both T and P cause a decrease in V
    • T causes an increase and P causes a decrease in V
    • T causes a decrease and P causes an increase in V
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11
Q

Avogadro’s Law

A
  • Mole - volume relationship
  • equal volume of different gases at the same temperature and pressure contain the same number of molecules.
  • Double the moles of gas at a fixed temperature and pressure, the volume of the gas doubles.
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12
Q

Molar gas volume

A
  • volume of one mole of gas
  • 1 mole of gas occupies 22.4 Liter at STP
  • Standard temperature and Pressure (STP) are 0ºC at 1 atm
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13
Q

Ideal gas law

A
  • Combination of Boyle’s, Charles’s and Avogadro’s laws
  • The ideal gas is a hypothetical gas that strictly obeys the simple gas laws and has the molar volume of 22.4 Liters at STP
  • Works at moderate pressures and for temp that are not too low. Breaks down at high pressure and very low temperature.
  • Formula: PV = nRT
    • P = pressure
    • V = Volume
    • n = number of moles of gas
    • R = molar gas constant at 0.082058 L • atm / (K • mol)
    • T = temperature in Kelvin
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14
Q

Gas density (Molecular mass determination)

A
  • Express gas densities in grams per liter rather than grams per milliliter.
  • Densities of gases depend on both temperature and pressure.
    • Volume of a fixed mass of gas depends upon temp and pressure.
  • Use the derivation of the formula, PV = nRT to find the molar mass (n) of the gas.
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15
Q

Determining the Molecular mass of a vapor

A
  • The ideal gas equation can be used to find the molecular weight (amu) or the molar mass (g/mol) of a volitile liquid
  • recall that molar mass = grams vapor / moles vapor
  • factors to consider: 1 mol / 22.4 L
  • assume that gases are at STP and behaving ideally
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16
Q

Gas Mixtures

A
  • each gas in the mixture exerts a pressure that is independent of the other gases present.
  • the gases behave as if they are alone in the vessel
17
Q

Dalton’s law of Partial Pressure

A
  • The sum of the partial pressures of all the different gases in a mixture is equal to the total pressure of the mixture. Ptotal = P1 + P2 + P3 + …
  • The individual partial pressures of the various gases is the pressure each individual gas would exert if it were alone in the container.
18
Q

Mole fraction

A
  • Component gas is the fraction of moles of that component in the total moles of gas mixture
  • or the fraction of molecules that are component molecules.
  • Pressure is proportional to moles at constant volume and temperature, so mole fraction equals the partial pressure divided by total pressure.
19
Q

Kinetic Molecular formula

A

Ek = 1/2mv2

Ek = Kinetic energy (Joules)

m = mass (kg)

v = velocity (m/s)

20
Q

Postulates of Kinetic Theory

A
  1. Gases are made up of tiny particles either atoms or molecules moving in constant motion.
  2. Volume of the particles is negligible compared to the total volume of gas, most of the volume is empty space.
  3. Gas particles act independently of each other, there are no attractive or repulsive forces between particles except when they collide.
  4. Collision of gas particles with each other or with the walls of the container are elastic. total kinetic energy of the gas particles is constant at constant temp. no kinetic energy is lost
  5. The average kinetic energy of a molecule is directly proportional to the Kelvin temp. the higher the temp, the greater the molecular kinetic energy.
21
Q

Qualitative Interpretation of Boyle’s Law

A
  • Smaller volume, more crowded, greater frequency of collision-more pressure.
  • Pressure increases, volume decreases.
22
Q

Qualitative Interpretation of Charles’ law

A
  • Temperature is a measure of the average kinetic energy of the gas particles.
  • Higher the temperature, the faster the gas particles move and more room is needed to avoid collision with the walls of the container.
  • Volume increases as temperature increases.
23
Q

Qualitative Interpretation of Avogadro’s law

A
  • More particles in a gas sample, more volume is needed by the particles to avoid increased collision with the walls of the container.
  • Volume increases as amount of sample increases.
24
Q

Qualitative Interpretation of Dalton’s law

A
  • Chemical identity of gas is not important
  • Total pressure of a fixed volume of gas dependss only on temperature T and total number of moles of gas
  • The pressure exerted by a specific kind of particle depend on the mole fraction of that kind of particle in the mixture.
25
Q

Molecular Speed

A
  • all gases have the same kinetic energy at the same temperature.
  • as the temperature increases, the average speed increases
  • the average translational kinetic energy of the molecule of a gas is directly proportional to the Kelvin temp.
  • From the kinetic energy equation, the lighter molecules have a greater velocity.
26
Q

Root-mean-square (RMS) molecular speed

A
  • Square root of the average of the squares of molecular speeds

Where: R = molar gas constant

T = absolute temperture

Mm = Molar mass for the gas so higher molar mass, lower rms speed

27
Q

Diffusion

A
  • Ability of two or more gases to mix spontaneously until they form a uniform mixture
  • Molecules of gas move fast but their travel is tortuous and zizag in nature because of frequent collision and change of course.
28
Q

Effusion

A
  • process by which gas molecules pass through a very small oriface or opening from a container at hight pressure to one at lower pressure.
29
Q

Who is Thomas Graham?

A
  • Scottish Chemist, 1805-1869
  • Observed that the rate of effusion of a gas is inversly proportional to the square root of its density.
30
Q

Graham’s law of effusion

A
  • in terms of molecular mass states that the rate of effusion of gas molecules from a particular hole is inversely proportional to the square root of the molecular mass of the gas at constant temperature and pressure.
  • Lighter the molecule, the more rapidly it effuses.
31
Q

Effusion of two gases

A
  • For two gases in the same container at the same temperature and pressure.
  • the faster the gas effuses, the less the time required for a given amout to effuse
  • Time required for effusion increases with molecular mass
32
Q

Real Gases

A
  • Ideal gas behavior fails at high pressure and/or low temperature.
  • At STP, the volume of gas particles are neglible compared to the total gas volume. Volume of a real gas at high pressure is larger than predicted. At highe pressures, particles are closer and intermolecular forces become important.
  • Most gases become liquids at high pressure and low temperature.
33
Q

Modification to the ideal gas laws

A
  • Ideal gas laws is based on the assumption that there is no intermolecular forces involved.
  • Van de waals equation
    • is an equation similar to the ideal gas law but includes two constants A and B to account for deviations from ideal behavior.
    • A and B are different for different gases must ne determined by experiment.
    • a = inter-molecule attraction
    • b = volume of molecule.

General Chemistry 1 (19 decks)

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