Chemistry midterm 2: Gases Flashcards
What is gas pressure caused by?
the force exerted by gas molecules colliding with surfaces of objects
What is atmospheric pressure caused by?
the weight of the column of air molecules in the atmosphere above an object
What is pressure?
the force exerted on a given area: P=F/A. Note that pressure is directly proportional to force and inversely proportional to area.
The SI unit for pressure is?
Pascal (Pa)= 1N/m^2
What is a barometer
A barometer is a glass tube that is closed at one end, filled with a nonvolatile liquid such as mercury, and then inverted and immersed in a container of that liquid. The atmosphere exerts pressure on the liquid outside the tube, the column of liquid exerts pressure inside the tube, and the pressure
at the liquid surface is the same inside and outside the tube. The height of the liquid in the tube is therefore proportional to the pressure exerted by the atmosphere.
What is hydrostatic pressure?
The pressure exerted by a fluid due to gravity. p=hpg. h= height of fluid, p= density, g= acceleration due to gravity
What is a manometer
is a device similar to a barometer that can be used to measure the pressure of a gas trapped in a
container
What is ideal gas?
a hypothetical construct that real gases approximate under
certain conditions
What is the ideal gas law
relates gas quantities for gases and is quite accurate for low pressures and moderate temperatures
What is Atomons/Gay Lussac’s law?
the pressure of a given amount of gas is directly proportional to its temperature on the kelvin scale when the volume is held constant
What is absolute 0
0 on the kelvin scale and the lowest possible temperature
What is Charles law?
the volume of a given amount of gas is directly proportional to its temperature on the kelvin scale when the pressure is held constant
Boyle’s law states?
The volume of a given amount of gas held at constant temperature is inversely proportional to the pressure under which it is measured.
Avogadro’s law states
For a confined gas, the volume (V) and the number of moles (n) are directly proportional if the pressure and temperature both remain constant.
What is partial pressure?
The pressure exerted by each individual gas in a mixture
What is Dalton’s law of partial pressures?
The total pressure of a mixture of ideal gases is equal to the sum of the partial pressures of the component gases
What is the mole fraction?
a unit of concentration defined as the number of moles of a component of a solution divided by the total number of
moles of all components
What is the vapour pressure of water
the pressure exerted by water vapor in equilibrium with liquid water in a closed container, depends on the
temperature
What is the mean free path?
the average distance a molecule travels between collisions. The mean free path increases with
decreasing pressure
What is diffusion?
the process by which molecules disperse in space in response to differences in concentration
What is the rate of diffusion?
the amount of gas passing through some area per unit time
What does the rate of diffusion depend on?
- the concentration gradient (the increase or decrease in
concentration from one point to another) - the amount of surface area available for diffusion
- the distance the gas particles must travel
What is effusion?
the escape of gas molecules through a tiny hole such as a pinhole in a balloon into a vacuum
What is the relationship between effusion and diffusion
Although diffusion and effusion rates both depend on the molar mass of the gas involved, their rates are not equal; however, the ratios of their rates are the same
What is Graham’s law of effusion?
The rate of effusion of a gas is inversely proportional to the square root of the mass of its particles
What is the kinetic moleuclar theory?
a simple microscopic model that effectively explains the gas laws described in previous modules of this chapter
What is the first postulate of KMT
Gases are composed of molecules that are in continuous motion, travelling in straight lines and changing
direction only when they collide with other molecules or with the walls of a container.
What is the second postulate of KMT
The molecules composing the gas are negligibly small compared to the distances between them
What is the third postulate of KMT
The pressure exerted by a gas in a container results from collisions between the gas molecules and the container walls.
What is the fourth postulate of KMT
Gas molecules exert no attractive or repulsive forces on each other or the container walls; therefore, their
collisions are elastic (do not involve a loss of energy).
What is the fifth postulate of KMT
The average kinetic energy of the gas molecules is proportional to the kelvin temperature of the gas.
How can KMT explain Amonton’s law
. If the temperature is increased, the average speed and kinetic energy of the gas molecules increase. If the volume is held constant, the increased speed of the gas molecules results in more frequent and more forceful collisions with the walls of the container, therefore increasing the
pressure
How can KMT explain Charles’s law
If the temperature of a gas is increased, a constant pressure may be maintained only if the volume occupied by the gas increases. This will result in greater average distances traveled by the molecules to reach the container walls, as well as increased wall surface area. These conditions will decrease both the frequency of molecule-wall collisions and the number of collisions per unit area, the combined effects of which balance the effect of increased collision forces due to the greater kinetic energy
at the higher temperature
How can KMT explain Boyle’s law
If the gas volume volume of a given amount of gas at a given temperature is decreased (that is, if the gas is compressed), the molecules will be exposed to a decreased container wall area. Collisions with the container wall will therefore occur more frequently and the pressure exerted by the gas will increase
How can KMT explain Avogadro’s law
At constant pressure and temperature, the frequency and force of molecule-wall collisions are constant. Under such conditions, increasing the number of gaseous molecules will require a proportional increase in the container volume in order to yield a decrease in the number of collisions per
unit area to compensate for the increased frequency of collisions
How can KMT explain Dalton’s law
Because of the large distances between them, the molecules of one gas in a mixture bombard the container walls with the same frequency whether other gases are present or not, and the total pressure of a gas mixture equals the sum of the (partial) pressures of the individual gases.
What is van der walls equation
The van der Waals equation improves upon the ideal gas law by adding two terms: one to account for the volume of the gas molecules and another for the attractive forces between them.
What is the compressibility factor (Z)
ratio of the experimentally measured molar volume for a gas to its molar volume as computed from the ideal
gas equation
Describe Maxwell-Boltzmann distribution
- in a gas sample, particles have various speeds.
- Because there are an enormous number of particles in a gas sample, the
molecular speed distribution and the average speed remain constant - The molecular speed distribution is known as a Maxwell-Boltzmann distribution
If the temperature of a gas sample increases, KE:
increases. more particles at higher speeds and distribution shifts toward higher speeds overall (to the right)
If the temperature decreases, the average KE
decreases. more particles at lower speeds and distribution shifts to the lower speeds overall
(to the left)
At a given temperature, all gases have the same
average kinetic energy
Molecular velocity is directly related to
molecular mass. At a given temperature, lighter particles
move faster on average than heavier particles
Describe some differences between solid, liquid, and gaseous states
- Particles in a solid are tightly packed together and often arranged in a regular pattern; in a liquid, they are close together with no regular arrangement; in a gas, they are far apart with no regular arrangement.
- Particles in a solid vibrate about fixed positions and do not generally move in relation to one another; in a liquid, they move past each other but remain in essentially constant contact; in a gas, they move independently of one another except when they collide
The difference of properties of solids, liquids, and gases are due to
the strengths of the attractive forces between the atoms, molecules, or ions that make up each phase
The phase in which a substance exists depends on the
relative extents of its
intermolecular forces (IMFs) and the kinetic energies (KE) of its molecules.
Which unit of pressure is referred to as the standard atmospheric pressure (exerted by the atmosphere on the earth’s surface due to gravity)
760mmHg= 1atm
