Gases

What is pressure?
Force applied per given area.
The units of pressure
atm, kpa, torr or mmHg
What is STP
standard temp and pressure Table A
237 K ~ 0 C
1 atm ~ 101.3 kPa 760 torr or 760 mmhg
kinetic molecular theory of gases
ideal gases
property #1
the gas molecules move in a continuous straight line w/ random movement.
property #2
there are no forces of attraction between molecules
property #3
molecules are so small they essentially have no volume.
property #4
collisions are elastic between gas molecules (elastic indicates no energy expanded)
property #5
there is a direct relationship between temperature and ave kinetic energy of a particle
which gases most resemble an ideal gas under most conditions: He
The lighter the gas, the more ideal it will act (therefore H2 and He act the most idea.
Real Gases
low volume
low temperature
low pressure
Ideal Gases
high volume
high temperature
high pressure
Boyles law:
relationship between pressure and volume of gas at constant temp and number of particles. A increase in pressure causes a decrease in volume.
Charles Law:
relationship between and volume of a gas
At constant pressure and number of particles. An increase in temperature causes an increase in volume.
Gay-Lussac’s Law
relationship between temp and pressure of gas. At constant volume and number of particles and an increase in pressure causes an increase of temperature.
Combines Gas Law
By combining all the laws for an ideal gas, we can solve for all 3 variables
(P1 X V1)/T1 = (P2 X V2)/T2
What is vapor pressure
1. Pressure that is exerted the container walls as collisions occur.
2. The greater the temperature the greater the vapor pressure
trends on table H
Temperature goes up
pressure goes up
What is the boiling point of water?
100 C
Mt Everest P525 torr 7 BP is lower because there are less air molecules applying pressure. Molecules vaporize more quickly.
If something is volatile does i have a low vapor pressure or a high vapor pressure?
High vapor pressure-it vaporizes quickly
*unstable and volatile substance have high vapor point.
What is boiling point?
1. The point at which all the molecules have enough energy to change into vapor.
2. When the vapor pressure of the liquid equals or exceeds atmosphere pressure, the boiling occurs.
What is Avogadro’s hypothesis?
Under the same conditions of temperature and pressure equal volumes of gasses contain the same number of particles.
Particles can be:
molecules
atoms
ions
What is the mole?
unit number of particles
1. 1 mole of particles equals the formula mass of the substance express in grams
2. 1 mole refers to 6.02 x 10 (23) particles.
What is molar volume?
1 mole of any gas will occupy a volume of 22.4 liters @stp
Which does not have a molar volume of 22.4 liters?
I2 (solid at STP)
Graham’s Law of Diffusion
At a given temperature and pressure the great the density of the gas the slow the gas diffuses. Effusion is the process of a gas escaping through small pores/openings. This pollows the same principle.
What is the law of partial pressure?
The total pressure in a container is equal to the sum of all the partial pressures of the gasses in the container.
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