GASES (chapter 10)By Dieu Ngo

Characteristics of Gases Essential for life Expand to fill container Compressible Readily flow Form homogeneous mixtures with other gases Vol of gases itself=smaller portion of total

volume at room temp. and pressure Noble gases=monotomic gases Diatomic gases Gases: molecular compounds, nonmetals Vapors

Properties of Gases

T- temperature (in K) V- volume (in L) n- quantity (in moles) P- pressure (in atm)

Gas Pressure

P=F/A Barometer-contains a column of mercury (Hg)

whose height is directly related to the pressure exerted by the atmosphere (mm Hg or torr)

Manometer- used to measure pressure in enclosed gases (usually below atm. Pressure); det’ed from the difference in heights of mercury levels in U-tube

Atmospheric Pressure

Caused by gravity Atoms of atm.=tiny massesoverride

gravitational forces Magnitude: F= ma a = 9.8 m/s^2

Standard Atmospheric Pressure

PRESSURE=1 atm = 760 mmHg = 760 torr = 1.013E5Pa = 101.3kPa

Pgas= Patm + Ph

Gas Laws

Boyle’s Law- V=contant/P (T, n) ;or P1V1=P2V2

Charles Law- V= constant x T (P, n); or V1/T1=V2/T2

Gay-Lussac’s Law- V= constant x n (P, T); or P1/T1=P2/T2

Ideal-Gas Equation

PV=nRT P in atm V in L n in moles T in K R is gas constant = 0.0821 L-atm/mol-K Combined: PV/T=PV/T

Standard temp. and pressure

STP: Pressure = 1 atm Temperature = 0 degrees Celsius =

273K Volume of 1 mol = 22.4 L

Dalton’s Law of Partial Pressure

The total pressure of a mixture of ideal gases is the sum of the individual pressures each ideal gas would exert if it were the only gas in the container

Pt =P1+P2+…+PN

Pi=niRT/V Pt=Pgas+PH2O

Mole Fraction (X) The ratio of the # of moles of a

component in a mixture of the total # of moles present

Xi = #of moles of component i / total # of moles in mixture

PA = (XA) (PT) Vol % of a gas in a mixture = mole

fraction of that gas

Kinetic Molecular Theoryof Gases

KMT- at the same temperature, molecules of all gases have the same average translational kinetic energy

rms speed is the square root of the average of the squared velocities of the gas molecules:

The average speed is the average of the velocities:

Temp increases speed increases The rms speed of a gas is inversely related to the

molar mass of the gas at a given temp:

Effusion

Is the flow of gas molecules through a small pinhole or small opening into a vacuum

Graham’s Law of Effusion relates the rates of 2 gases escaping through the same pinhole and their molar masses at constant temperature

Lalalalalalala… chemistry!

Diffusion- A process in which a substance gradually mixes with another

Mean Free Path- the average distance gas molecules travel between collisions

Gas molecules vs. ideal gas Gas molecules- attracts at short distances

do not collide with walls of container like ideal gas

Cause the experimental gas pressure to be less than the ideal-gas pressure

Vol for gas to move in container < total vol of container

Van der Waals equation: