Chapter 5 - Gases Flashcards
Gas molecules are constantly in
Motion
As they move and strike the surface they ___ on the surface
Push (push = force)
The pressure of gas would be
The total amount of force extorted by gas molecules hitting the entire surface at any one instant
Pressure formula
Force / Area
Whenever there is a pressure difference, a gas will flow from an area of ___ pressure to an area of ___ pressure
High to Low
Differences in air pressure result in
Weather and wind patterns
The ___ in the atmosphere you climb, the ___ the atmospheric pressure is around you
Higher, Lower
If there’s a difference in pressure across the eardrum membrane, the membrane will be
Pushed out (popped eardrum)
What does the pressure of a gas depend on?
- Number of gas particles in a given volume
- Volume of the Container
- Average Speed of the gas particles
Air pressure is measured with a
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
What happens to the height of the column of mercury in a mercury barometer as you climb to the top of a mountain?
The height of the column decreases because atmospheric pressure decreases with increasing altitude
Atmosphere (atm) =
1) millimeters of mercury (mmHg)
2) Torr (torr)
1) 760 mmHg
2) 760 torr
The pressure of a gas trapped in a container can be measured with an instrument called
Manometer
In a manometer, the difference in the liquid levels is a measure of the difference in
Pressure between the gas and the atmosphere
Boyle’s Law
- 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
Boyle’s Law and Diving
Because water is more dense than air, for each 10m you dive below the surface, the pressure on your lungs increases 1 atm.
If a driver holds her breath and rises to the surface quickly
She should exhale, to avoid the volume expanding by a factor of 3 which causes damage to internal organs
Charles’ Law
- Volume is directly proportional to temperature.
- As T increases, V also increases.
- V = constant x T.
Charles’ Law and Absolute Zero
• 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.
Avogadro’s Law
- 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)
Ideal Gas Law
• 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
What are the Standard Conditions?
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
Standard Conditions
- STP
- Standard pressure = 1 atm
- Standard temperature = 273 K (0C)
Molar Volume
- 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
Density at Standard Conditions
- 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
Density id directly proportional to
Molar Mass
Molar Mass of a Gas
- 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
Mixture of Gases
- 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
The pressure of a single gas in a mixture of gases is called its
Partial pressure
The sum of the partial pressures of all the gases in the mixture equals the Total Pressure
Dalton’s Law of Partial Pressures
Kinetic-molecular theory says that
The gas molecules are negligibly small and don’t interact
Because the gas molecules are not sticking together, each gas molecule contributes its own force to the total force on the side
Dalton’s Law and Pressure
Gases in the same container have the same temperature, therefore
They have the same average kinetic energy
If gases have different masses, the only way for them to have the same kinetic energy is to have
Different average velocities
All the gas molecules in a sample can travel at different speeds. However, the distribution of speeds follows a statistical pattern called a
Boltzman Distribution
As the absolute temperature increases,
The average velocity increases
The average distance a molecule travels between collisions is called the
Mean Free Path
As the pressure increases
The mean free path decreases
The process of a collection of molecules spreading out from high concentration to low concentration is called
Diffusion
The process by which a collection of molecules escapes through a small hole into vacuum is called
Effusion
The rates of diffusion and effusion of a gas are both related to
It’s rms average velocity
For two different gases at the same temperature, the ratio of their rates of effusion is given by an equation
Graham’s Law of Effusion
Ideal gas laws assume
- No attractions between gas molecules
* Gas molecules do not take up space (based on the kinetic-molecular theory)
Real gases often do not behave like ideal gases at
High pressure or low temperature
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.
Molecular Volume, Intermolecular Attractions
____ modified the ideal gas equation to account for the molecular volume and intermolecular attractions
Van Der Waals Constant
The ____ is the layer closest to the Earth’s surface (circular due to thermal currents.
Troposphere (weather)
The ____ is the next layer up (less air mixing)
Stratosphere
The boundary between the troposphere and stratosphere is called the
Tropopause
The ___ ___ is a layer of high O3 concentration located in the stratosphere
Ozone Layer
