Chapter 5 - Gases

Question 1

Gas molecules are constantly in

Answer 1

Motion

Question 2

As they move and strike the surface they ___ on the surface

Answer 2

Push (push = force)

Question 3

The pressure of gas would be

Answer 3

The total amount of force extorted by gas molecules hitting the entire surface at any one instant

Question 4

Pressure formula

Answer 4

Force / Area

Question 5

Whenever there is a pressure difference, a gas will flow from an area of ___ pressure to an area of ___ pressure

Answer 5

High to Low

Question 6

Differences in air pressure result in

Answer 6

Weather and wind patterns

Question 7

The ___ in the atmosphere you climb, the ___ the atmospheric pressure is around you

Answer 7

Higher, Lower

Question 8

If there’s a difference in pressure across the eardrum membrane, the membrane will be

Answer 8

Pushed out (popped eardrum)

Question 9

What does the pressure of a gas depend on?

Answer 9

• Number of gas particles in a given volume
• Volume of the Container
• Average Speed of the gas particles

Question 10

Air pressure is measured with a

Answer 10

Barometer
• Column of mercury supported by air pressure
• Force of the air in the surface of the Mercury counter balances the force of gravity on the column of mercury

Question 11

What happens to the height of the column of mercury in a mercury barometer as you climb to the top of a mountain?

Answer 11

The height of the column decreases because atmospheric pressure decreases with increasing altitude

Question 12

Atmosphere (atm) =

1) millimeters of mercury (mmHg)
2) Torr (torr)

Answer 12

1) 760 mmHg

2) 760 torr

Question 13

The pressure of a gas trapped in a container can be measured with an instrument called

Answer 13

Manometer

Question 14

In a manometer, the difference in the liquid levels is a measure of the difference in

Answer 14

Pressure between the gas and the atmosphere

Question 15

Boyle’s Law

Answer 15

• Pressure of a gas is inversely proportional to its volume
• As P increases, V decreases by the same factor
• P x V = Constant
• P1 x V1 = P2 x V2

Question 16

Boyle’s Law and Diving

Answer 16

Because water is more dense than air, for each 10m you dive below the surface, the pressure on your lungs increases 1 atm.

Question 17

If a driver holds her breath and rises to the surface quickly

Answer 17

She should exhale, to avoid the volume expanding by a factor of 3 which causes damage to internal organs

Question 18

Charles’ Law

Answer 18

• Volume is directly proportional to temperature.
• As T increases, V also increases.
• V = constant x T.

Question 19

Charles’ Law and Absolute Zero

Answer 19

• If you plot volume vs. temperature for any gas at constant pressure, the points will all fall on a straight line.
• If the lines are extrapolated back to a volume of “0”, they all show the same temperature
(-273.15C) called Absolute Zero.

Question 20

Avogadro’s Law

Answer 20

• Volume is directly proportional to the number of gas molecules.
• V = constant x n
• Count number of gas molecules by moles
• Equal volumes of gases contain equal numbers of molecules (the gas doesn’t matter)

Question 21

Ideal Gas Law

Answer 21

• R is called the Gas Constant
• The value of R depends on the units of P and V
• (P)(V) / (n)(T) = R
OR PV = nRT

Question 22

What are the Standard Conditions?

Answer 22

Because the volume of a gas varies with pressure and temperature, chemists have agreed on a set of conditions to report our measurements so that comparison is easy

Question 23

Standard Conditions

Answer 23

• STP
• Standard pressure = 1 atm
• Standard temperature = 273 K (0C)

Question 24

Molar Volume

Answer 24

• Solving the ideal gas equation for the volume of 1 mil of gas at STP gives 22.4L
• We call the volume of 1 mole of gas at STP molar volume
• It is important to recognize that one mole measures of different gases have different masses even though they have the same volume

Question 25

Density at Standard Conditions

Answer 25

* Density is the Ratio of Mass to Volume * Density of a gas is generally given in g/L * The volume of 1 mole at STP = 22.4L * Density = (Molar Mass, g) / 22.4L

Question 26

Density id directly proportional to

Answer 26

Molar Mass

Question 27

Molar Mass of a Gas

Answer 27

* One of the methods chemists use to determine the molar mass of an unknown substance is to heat a weighed sample until it becomes a gas, measure the temperature, pressure, and volume, and use the ideal gas law * Molar Mass = Mass in grams / Moles

Question 28

Mixture of Gases

Answer 28

* When gases are mixed together, their molecules behave independent of each other * Therefore, in certain application the mixture can be thought of as one gas

Question 29

The pressure of a single gas in a mixture of gases is called its

Answer 29

Partial pressure

Question 30

The sum of the partial pressures of all the gases in the mixture equals the Total Pressure

Answer 30

Dalton’s Law of Partial Pressures

Question 31

Kinetic-molecular theory says that

Answer 31

The gas molecules are negligibly small and don’t interact

Question 32

Because the gas molecules are not sticking together, each gas molecule contributes its own force to the total force on the side

Answer 32

Dalton’s Law and Pressure

Question 33

Gases in the same container have the same temperature, therefore

Answer 33

They have the same average kinetic energy

Question 34

If gases have different masses, the only way for them to have the same kinetic energy is to have

Answer 34

Different average velocities

Question 35

All the gas molecules in a sample can travel at different speeds. However, the distribution of speeds follows a statistical pattern called a

Answer 35

Boltzman Distribution

Question 36

As the absolute temperature increases,

Answer 36

The average velocity increases

Question 37

The average distance a molecule travels between collisions is called the

Answer 37

Mean Free Path

Question 38

As the pressure increases

Answer 38

The mean free path decreases

Question 39

The process of a collection of molecules spreading out from high concentration to low concentration is called

Answer 39

Diffusion

Question 40

The process by which a collection of molecules escapes through a small hole into vacuum is called

Answer 40

Effusion

Question 41

The rates of diffusion and effusion of a gas are both related to

Answer 41

It’s rms average velocity

Question 42

For two different gases at the same temperature, the ratio of their rates of effusion is given by an equation

Answer 42

Graham’s Law of Effusion

Question 43

Ideal gas laws assume

Answer 43

* No attractions between gas molecules | * Gas molecules do not take up space (based on the kinetic-molecular theory)

Question 44

Real gases often do not behave like ideal gases at

Answer 44

High pressure or low temperature

Question 45

The ___ ___ makes the real volume larger than the ideal gas law would predict. the ___ ___ make the real pressure less than the ideal gas would predict.

Answer 45

Molecular Volume, Intermolecular Attractions

Question 46

____ modified the ideal gas equation to account for the molecular volume and intermolecular attractions

Answer 46

Van Der Waals Constant

Question 47

The ____ is the layer closest to the Earth’s surface (circular due to thermal currents.

Answer 47

Troposphere (weather)

Question 48

The ____ is the next layer up (less air mixing)

Answer 48

Stratosphere

Question 49

The boundary between the troposphere and stratosphere is called the

Answer 49

Tropopause

Question 50

The ___ ___ is a layer of high O3 concentration located in the stratosphere

Answer 50

Ozone Layer