average molecular velocity

The molecular velocity is inversely proportional to the square root of the mass of the particle -- net-net, the lightest particles move fastest -- make sense? Fortunately, since they are all being considered at once, you can estimate without taking the square root: just compare the molecular (or in one case atomic) mass:

H2O = 18.02 g/mole
He = 4.00 g/mole
HCl = 36.46 g/mole
BrF = 98.90 g/mole
NO2 = 46.00 g/mole

So in increasing order, you have BrF < NO2 < HCl < H2O < He

Hope that helped!

Some examples about conversions in chemistry

Q :- 
1. How many moles of methanol, CH3OH are there in 6.53x10^23 molecules of methanol?
2. How many formula units of sodium chloride are in 16.0 grams of sodium chloride?
3. How many atoms are in 145.6L of neon gas?
4. How many liters L of gas are there if there are 2.7x10^24 fluorine molecules?
5. There 3x10^24 atoms of hydrogen in a large container. How many molecules of hydrogen are there? How many liters of hydrogen gas?


A:- 
 1. divide the given number by Avogadro's number to get answer to first one.

2. In 16 grams, the number of formula units are: given wt/mol. wt = 16/58= 0.28 approx.

3. Good question. in 22.4 dm^3, it's one mole, for neon, so divide given volume by 22.4 dm^3 (1dm^3=1 L). Now multiply what you get by Avogadro's Number. This is number of atoms in the given sample.

4. This is pretty interesting. See:
First, divide given number by Avogadro's number then you'll get number of moles. Now for Fluorine, a diatomic element, we need to find what volume corresponds to one mole, so divide the value 22.4 by its valency 2, so its 11.2 litres, now the number of moles you got previously in this problem, go multiply this 11.2 with that number, you'll get the volume.

5. Here 3/2 x 10^24 molecules exist, as hydrogen normally exists in diatomic molecular form. Also, as in earlier problem divide the number of MOLECULES with Avogadro's number and then multiply the result by 11.2. You get the required volume of hydrogen in the container

The Phases of Matter

We are all familiar with solids, liquids and gases. Whether a substance is a solid, liquid or gas depends on the potential energy in the atomic forces holding the particles together and the thermal energy of the particle motions. The pressure on the subtance also has an effect on the phase.

Solids

Crystaline Solids

Crystaline solids are characterised by a long-range order. The atoms are closely packed on lattice points held in in place by atomic bonds. The internal energy of the atoms is not sufficient to allow the atoms to break away from their lattice positions. Examples of crystaline solids include semiconductors, quartz, salt, etc.

Amorphous Solids

Amorphous Solids are still closely packed together but lack the translational symmetry of crystaline solids. However, even amorphous solids have relatively good spatial ordering, especially over small distances, (10-100 molecules)

Liquids

As the material is heated, the internal energy is increased and the atoms are no longer tied to their lattice positions but can move relative to each other although the atoms are still closely packed together.

Gases

A gas is matter in which the molecules are widely separated, move around freely, and move at high speeds. Examples of solids include the gases we breathe (nitrogen, oxygen, and others), the helium in balloons, and steam (water vapor).

Plasmas

Eventually, given enough heat, the electrons and nucleus become separated and into positively, charged ions and negatively charged electrons. This soup of ions and electrons is known as a plasma