Matter - States of Matter

Matter is anything that has mass and takes up space (to use an old freshman chemistry definition). In physical chemistry we will mainly be concerned with matter that is built up from protons, neutrons and electrons. We rarely will be concerned with the more exotic forms of matter like positrons and mesons and essentially never with quarks. The matter we are most concerned with is made when protons, neutrons and electrons are put together to form atoms and molecules.

Matter exists in several possible states. The most common states of matter on the surface of our planet are:

solid
liquid
gas.

plasma (ionized gases)
nuclear matter (as in neutron stars)
white dwarf stars
interfacial matter (Material at surfaces often has different properties than bulk matter.)
"black hole" matter
etc.

Variables To Describe Matter

We can describe a sample of matter by using variables such as mass, number of moles, volume, temperature, pressure, density and so on. we usually symbolize these variables as (respectively) m, n, V, T, p, r (lower case Greek "rho"), and so on. These variables are called "state variables" because they describe the state of the system and because they depend only on the state of the system. We will be defining more state variables as we go along.

Variables describing matter can be divided into two classes. Variables whose value is proportional to the amount of sample are called extensive variables and variables which are independent of the amount of sample are called intensive variables. (You can remember these by letting the word extensive remind you of the word "extent and letting intensive remind you of intensity and vice versa.)

In the above list you should convince yourself that m, n, and V are extensive and T, p, and r are intensive.

The state of a system is given by specifying the values of all the variables describing the system. This definition of "state" assumes that the system is at equilibrium. We will give a proper thermodynamic definition later, but for now we define equilibrium by saying that everything that wants to happen in the system has happened. Another way to say this is to say that the system has the properties it would have after infinite time. You could say that equilibrium is the state when none of the values of the variables is changing in time, but here you have to be careful to exclude "steady-state" systems. (An example of a steady-state system is one where material is flowing in and out of the system, but the system itself appears not to be changing.)
 

Units and Dimensions

We will mostly use the SI (Système International d'Unités) system of units.  Some exceptions are listed below. The SI system is the standard system of units in the world today. It is an outgrowth of the old mks system. The system is metric in nature, meaning that larger or smaller units are obtained by multiplying or dividing a base unit by powers of ten. There is an excellent description of the SI system, with all of the details (including prefixes), at the NIST website. (NIST also has a list of all of the fundamental constants.)

We will use some non-SI units. It is important to know that all non-SI units are now defined in terms of SI units.

For volume we will use liters (L) and mL.  There are 1000 L in a m³.

For energy we will occasionally see liter atmospheres (Latm) or liter bars (Lbar). You need to convince yourself that a pressure times a volume has units of energy. Some of our calculations will give us answers in Latm. These should always be converted to Joules.

1 Latm = 101.325 J

1 Lbar = 100 J

1 atm = 101325 Pa = 1.01325 bar = 760 Torr.

The Torr is written in the older literature as mmHg.

We will not often use English units for length, but it is sometimes useful to know that the inch is defined as exactly 0.0254 m ( or 2.54 cm).

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