Chapter 9: gases

Pressure

force per unit area

vacuum

empty space with no gas molecules present

atmospheric pressure

The pressure exerted by gas molecules in Earth's atmosphere. Gravity pulls atmospheric gases downward, creating a force on everything it touches. Decreases as altitude increases (air becomes "thinner" because there is less overlying mass).

Standard atmospheric pressure:

760 torr at 0˚C at sea level

conversion for units of pressure

1 atm = 760 torr = 760 mmHg = 101.325 kPa

normal atmospheric conditions

25 ℃ and 1 atm

Elements that are gases at normal atmospheric conditions (have no fear of clever ozone)

H₂,N₂, O₂, F₂, Cl₂ , O₃, + all noble gases

molecules that are gases at normal atmospheric conditions

CO, CO₂, HCl, NH₃, CH₄. No ionic compounds exist as gases

How does the atmosphere cause objects to burn up?

Anything entering from space hits the layer of gas molecules pulled down by gravity, causing friction and extreme heat.

What happens to atmospheric pressure as altitude increases?

It decreases. Air becomes thinner because there are fewer gas molecules at higher altitudes.

How does the body adapt to altitude training, and how long does it last?

The body adapts to low oxygen to improve oxygen transport, and these changes persist for about two weeks after returning to sea level.

1 inch

2.54 cm

if the volume of a container increases, pressure_______

decreases. pressure and volume are related inversely

if temperature increases, pressure ________

increases. pressure and temperature are directly related

if the number of gas molecules increases, pressure _______

increases. pressure and number of molecules are directly related

Combined gas law

(P_iV_i / T_i )= (P_fV_f / T_f ).

T must be in kelvins!

Standard temperature and pressure (STP)

T = 0.00 ℃ and P = 1.00 atm

Ideal gas law

PV = nRT

The molar volume of any ideal gas at STP

22.4L/mol

dalton’s law of partial pressure

P_total = P_{1 +} P₂ + P₃ + …… (total pressure of a mixture of gases = sum of the partial pressure of gases present)

Partial pressure

the pressure exerted by all the particles of one type of gas

mole fraction (x_A)

(# moles of gas A) / (Total # moles of all gases in the mixture)

partial pressure (P_n) of the n^th gas is calculated as follows:

P_n = X_n P_total

kinetic energy (KE) formula

½ * (mass)(velocity)²

root-mean-square velocity

U_rms = √(3RT/MM). The higher the molar mass of a particle (MM) the slower it moves

hypoxia

a condition where the body does not have a sufficient oxygen supply, which can lead to dizziness, headache, and shortness of breath

oxygen toxicity

when P_O2 (partial pressure of oxygen) > 1.4 atm, oxygen toxicity occurs, resulting in muscle twitching, tunnel vision, and convulsions

nitrogen narcosis

nitrogen narcosis occurs when P_N2 (partial pressureo of nitrogen gas) > 4 atm which can make a diver feel tipsy

particle volume

gas molecules are so small they occupy no volume

particle motion

gas molecules move in constant, random motion. The pressure exerted by the gas results from collisions with the gas particles and the walls of its container

particle attraction

gas molecules do not attract or repel one another. they do not affect the motion of other particles except upon collision

particle collisions

collisions are perfectly elastic. energy is totally transferred from one molecule to another, and the overall energy of the system remains the same; no energy is lost to friction

the average kinetic energy of the molecules is __________ to the absolute temperature of the gas in Kelvins

proportional

at higher temperatures, gas molecules move more __________

quickly

at lower temperatures, gas molecules move more __________

slowly

more massive molecules move ______ than lighter molecules at the same temperature

slower

Graham’s law of effusion

rate of effusion of molecules ∝ 1/√MM_gas . the rate varies inversely with the square root of the molar mass (MM)

Graham’s law of effusion for 2 gases

rate of effusion for Gas 1 / rate of effusion for Gas 2 =

√MM_gas2 / √MM_gas1 =

time for Gas 2 to effuse / time for Gas 1 to effuse

What does Kinetic molecular volume theory assume about the volume occupied by gas particles if they behave ideally?

No volume for individual particles

When the volume of a container is so large that the volume occupied by a gas is negligible by comparison, gas pressure is likely to be ______.

low

Effusion

process of a gas under pressure escaping from a container via a small opening

Diffusion

gradual mixing of molecules of one gas with molecules of another gas by virtue of their kinetic properties

What does Kinetic Molecular Theory assume about attractive forces between gas particles if the gas behaves ideally?

there are no attractive forces between the gas particles

The attractive forces between gas particles is more likely to be negligible when temperature is ________.

high

Indicate for what conditions a gas is more likely to behave ideally.

Pressure is low , and temperature is high

If the volume occupied by gas particles in a non-ideal gas is not

negligible, the actual volume in which the gas particles can move is ___.

smaller

If the gas particles in a non-ideal gas experience attractive forces,

then the actual pressure exerted by the gas particles is ________

lower