States of Matter

General Principles

S.I. Units

These basic quantities are vital within physical chemistry (and obviously just in general).
It is also important to automatically understand the magitudes of various quantities. A chemist in general needs to know from mega- to femto- (or even atto-), i.e. the very small scale. A dirty physicist ( :P ) on the other hand needs to be aware of the macro scale of objects.

File:Time scale of molecular interactions.png

Time scale of molecular interactions.


Quantity	Unit	S.I. Unit	Symbol
Mass	Kilogram	YES	kg
Time	Seconds	YES	s
Length	Meter	YES	m
Electrical Potential	Volt	YES	V
Temperature	Kelvin	YES	K
Temperature	Degrees Celcius	NO	°C
Moles	Mole (6.02 x 10²³ molecules)	YES	mol
Energy	Joules	YES	J
Velocity	Meters/second	YES	ms^-1
Force	Newton	YES	kgms^-2 (N)
Pressure	Pascal	YES	kgm^-1s^-2 (Nm^-2 = Pa)
	Bar	NO	1 bar = 10⁵ Pa
	Atmosphere	NO	1 atm = 1.01325 bar
	Torr	NO	1 atm = 760 Torr (1 Torr = 1 mmHg)


Magnitude (prefix)	Mathematical Description
Mega	10⁶
Kilo	10³
Centi	10^-2
Milli	10^-3
Micro	10^-6
Nano	10^-9
Pico	10^-12
Femto	10^-15
Atto	10^-18

Physical States


State	Description
GAS	Distance travelled between “collisions” is large compared to the size of the particle. Particles are free to move past each other - they have unimpeded movement.
LIQUID	Distance travelled between “collisions” is comparable to the size of the particle. Particles are able to move past each other - “jostling with movement”.
SOLID	Distance travelled between “collisions” is less than the size of the particle - continuous collisions. Particles are unable to move past each other - "jostling" but no movement.

Properties of Gases

A gas, as described previously, is a substance whose molecules are free too move without hindrance. Like liquids, they are capable of filling any container they're in.
The difference between a gas ana a liquid is simply that gas particles have a lot of space and time separating molecule collisions.
This has led scientists to question what the properties of a perfect gas are.

The Ideal Gas Law

A perfect (or ideal) gas is in fact a hypothetical substance, for it does not take into account molecular interactions that real gases experience.
The ideal gas law is one of the most important equations to know. It is given below:

$P V = n R T$

where:

P = pressure (Pa)
V = volume (m³)
n = number of moles (mol)
R = Universal Gas Constant (J mol^-1 K^-1)
T = temperature (Kelvin)

Its derivation can be summarised by the combination of three important observations:


Physical Law	Observation	Symbolic Description
Charles' Law	At a constant pressure, the volume of a gas varies linearly with temperature.	$V = c o n s t a n t \times T$ at constant n, T
Boyle's Law'	At a constant temperature, the pressure of a fixed amount of gas is inversely proportional to its volume.	$P \times V = c o n s t a n t$ at constant n, V
Avogadro's Principle	At a given pressure and temperature, equal volumes of gas contain the same number of molecules. This introduces the concept of molar volume, i.e. the volume occupies by 1 mol of gas (V_m).	$V = c o n s t a n t \times n$ at constant P, T $V_{m} = V \div n$

Boyle's Law and Charles' Law are examples of limiting laws, in other words they can only be applies to a certain range - in this case from $p \to 0$