The Boring States of Matter CH11

Kinetic Energy EK

The energy an object has because of its motion.

Temperature is a measurement of average kinetic energy.

Kinetic Theory-

Tiny particles in all forms of matter are in constant motion.

Liquids vs. Gases

Liquids, the molecules are moving and touching.

They interact

They take up less space than gasses

They overall have less Ek

than a gas of the same substance

Gases, the molecules bounce off each other, but do not stay in contact

There is very little interaction between molecules

They take up a lot of space

 

Which of these 2 parts are compressible?

Can you “squish” the gas?

Can you “squish” the liquid?

gas

liquid

Evaporation: conversion of a liquid to a gas

At the surface, there are a few molecules that have enough Ek to escape to gas.

By increasing the temperature, more molecules will have the necessary Ek and evaporation will occur faster than before.

The vapor pressure increases with more heat/ Ek

Average kinetic energy

Temperature is a measurement of average kinetic energy.

If a beaker of water reads 20°C, do all molecules in the beaker have kinetic energy = 20⁰C? There is a broad range of kinetic

energies. Most of the molecules are “around 20C”, but there are some

significantly less energetic, and some significantly more energetic.

Solids Molecules in

solids only vibrate in place, they do not slide past each other

They interact in their FIXED position

More dense than gas, and most liquids

Salt crystal, atoms are in a set position

Heating a solid

The vibrations increase

If they vibrate enough, some of the bonds holding the solid together will break.

This is called the melting point.

S L melting

L S freezing

L G vaporization (or evaporation)

G L condensation

Evaporation vs. Boiling point Atm is pressing down on the surface

Solid to a Gas?…Sublimation

Solids also have a vapor pressure.

When vapor pressure is high enough, the solid will go to gas, without stopping at liquid.

This is called sublimation.

Gas to a solid – DEPOSITION

Dry ice, is a classic example of sublimation

Phase Transition names

SL

LS

L G

GL

S G

GS d

Melting Freezing

Vaporization Condensation

Sublimation deposition

Give the change of state for each term

Ionic Solids

Strong forces between oppositely charged ions.

HIGH melting points HIGH boiling points Non conductors as

solids, conductors while molten.

Often water soluble Depends upon attractive

forces for each other and other molecules.

Molecular Combination of 2 or more non metals

Molecular substances have 3 important types of weak intermolecular forces

1. Dispersion Forces

2. Dipole Forces

3. Hydrogen bonds

Inter-molecular (between molecule) forces are weak.

Therefore easy to separate:

Have low melting and boiling points Think Oxygen and Water They’re gases and liquids

at room temperature Non-Conductors of

electricity

Dispersion (London) Forces

Most common type of intermolecular force.

Caused by temporary induced- dipoles formed in adjacent molecules.

All molecules have dispersion forces, the strength depends on 2 factors: *The # of electrons in the

molecule

As molar mass increases, dispersion forces become stronger, the boiling pt of non-polar molecules increases.

Think of the electron cloud being agitated

F2 -188

Cl2 -34

Br2 59

I2 184

Dipole Forces

Electrically attractive forces between + and – end of adjacent polar molecules.

Boiling points of N2 -196C O2 -183C

NO -151C

The Nitrogen Monoxide is slightly polar and therefore has weak dipole forces. This explains the relatively higher melting points.

Hydrogen Bonding

Unusually strong DIPOLE forces.

This is due to the very small Hydrogen atom’s

Electronegativity difference with:

F fluorine

O oxygen

N nitrogen

The strongest of the ‘weak forces’

Water H2O bp = 100 C, H2S -61C

Putting it all togetherHow can you know if a substance will melt, or sublimate?

The transitions depend upon both pressure and temperature.

At a given Temperature T: At a low pressure, something might sublimate, at a

higher pressure it would likely melt

Phase diagram

solid

liquid

gas

Pressure

temperature

Triple point, all 3 phases exist simultaneously

Phase Diagram for Water

Triple point

.006 atm

.001C

4th state of matter: Plasma

Plasma

Occurs at super hot temperatures

Gas atoms are stripped of their electrons

Mix of loose electrons, and + gas ions is

called PLASMA

Hot plasmas make up the stars, and can be 10 million degrees

Not very relevant to HS Chemistry.

Maxwell-Boltzman Distrubution

At high T

More molecules are in a higher energy state