Phases of MatterProperties of a Gas

Edward A. Mottel

Department of Chemistry

Rose-Hulman Institute of Technology

Properties of Gases

Reading Assignment:• Zumdahl, Chapter 5.1-5.3

This lecture introduces the interrelated dependence of moles, temperature, pressure and volume of a confined gas.

Based on assumptions of ideal gas behavior, these parameters when combined form the ideal gas equation, PV=nRT.

Phases of Matter

Gases Liquids Solids Plasma

Gases

Large intermolecular distances,compared to molecular size

No long or short rangestructural order

GasesMix together in any proportions

Intermolecular collisions are elastic --energy is transferred through collisions

LiquidsSmall intermolecular distances --molecules are "touching"

Molecules may be orderedwith respect to each otherover a short range, but nolong range structural order

Energy is transferredthrough molecular vibration

Liquids

May or may notbe miscible

Liquids

Aqueous solutions are like liquids,except solute is surrounded by solvent

SolidsSmall intermolecular distances --molecules are "touching"

Long and shortrange structural orderin crystalline solids

Energy is transferredthrough molecular vibration

Solids

Amorphous solidshave less structural order

Solids

Very limited miscibilitywhile remaining in the solid state

Solids

Frozen solutions are possibleand called solid solutions

Plasma

High energy state in which all molecules are broken into constituent atoms, and most or all of the electrons are stripped from the atom

Very high temperature (106 K), condensed, gas-like phase consisting of nuclei and electrons

Plasma

Nuclei mix together in any proportions Applications occur in a few analytical

detection techniques and nuclear reactions Not involved in typical chemical reactions

Physical Properties of Matter

Temperature Pressure Volume Moles

Temperature

Temperature is a measure of molecular motion: vibration, rotation and translation

Gases move at high velocity• (> 1000 m·sec–1)

Common units:• Celsius (°C), Fahrenheit (°F)

Temperature

Absolute units: Kelvin (K), Rankine (°R) 0.00 °C = 273.15 K

= 32.00 °F = 491.67 °R 100.00 °C = 373.15 K

= 212.00 °F = 671.67 °R Isothermal - constant temperature

Pressure

Due to moleculeshitting the surface

Force per unit area

Pressure

What do you knowabout

the pressurein a balloon?

Pressure

Within a closed containerwith a flexible ormoveable barrier,

the external forcespushing on thesurface of the

containercontaining

the gas

are equal to the pressure of the trapped gas pushing out.

Barometer

mercury

vacuumWhat forces determinethe height of themercury in theglass tube?

atmosphericpressure

What forces determinethe height of themercury in theglass tube?

Barometer

Barometer

760 mm 30 inHow much pressuredoes the atmosphereexert?

Hg = 13.6 g·cm–3

= 0.490 lb·in–31.03 kg·cm–2

= 14.7 lb·in–2

Barometer

H2O= 1.0 g·cm–3

33 feetWhat is different ifwater is used as thefluid, rather thanmercury?

Pressure

Common units:• lbs·in–2, atmospheres (atm), mm Hg, torr,

pascals (N·m–2, Pa) 1.00 atm = 14.7 lbs·in–2

= 760 mm Hg = 760 torr

= 1.013 x105 Pa

Pressure

The actual atmospheric pressure is a function of the weather (high or low pressure) and altitude.• Typical Terre Haute pressure is 730-750

mm Hg. Isobaric - constant pressure

Volume

Gases occupy the complete volume to which they are constrained

Liquids and solids occupy a volume corresponding to their mass and density

Isochoric - constant volume

Moles

A counting unit for the number of molecules being considered

Physical Laws of Gases

Boyle's Law Charles' Law

Avogadro's Law Ideal Gas Law

Boyle's Law

P·V = constant

isothermalconstant amount of gas

volu

me

pressure

What does a plot of thisrelationship look like?

Charles' Law

VT

isobaricconstant amount of gas

volu

me

temperature

What does a plot of thisrelationship look like?

What does the y-interceptindicate?

Avogadro's Law

Vn

isobaricisothermal

volu

me

moles of gas

What does a plot of thisrelationship look like?

Gas Lawsvo

lum

e

pressure

Boyle

volu

me

temperature

Charles

volu

me

moles of gas

Avogadro

V 1/P V T V n

V nT

P

Ideal Gas Law

P·V n·T PV = nRT

• where R = ideal gas constant

= 0.08206 L·atm·mol–1·K–1

Boyle's Law

P·V = constant

isothermalconstant amount of gas

volu

me

pressure

How will this plot changeif the same number of moles

of gas are at ahigher temperature?

Common GasesRoom Temperature, One Atmosphere Pressure

Monatomic: He, Ne, Ar, Kr, Xe, Rn Polyatomic

• Elements: N2, O2, O3, F2, Cl2• Compounds: CO, CO2, NO, N2O, NO2,

N2O4, N2O5, CH4, C2H6, C2F4, etc.

Atmospheric Composition

Dry air

78% N2, 21% O2, 1%Ar Normal air

N2, O2, Ar, 0.03% CO2, 1.6% H2O