1. Chapter 12: Gases Kinetic-Molecular Theory
Gases are composed of tiny particles, with little or no attractive forces, separated by empty space.
Gas particles are in constant, random, straight-line motion, with perfectly elastic collisions.
A perfectly elastic collision passes 100% of energy.
KE=1/2 mv2 where average temperature tells KE.
Gases are compressible and take the shape of their container.
Gases effuse and diffuse based upon Graham’s law of diffusion…

2. Graham’s Law Example
Compare the rate of diffusion of hydrogen and oxygen.
Look up the GAM of helium and the GMM of nitrogen…. H2=2.0 g/mole and O2=32.0 g/mole.
So…the rate of H2 is 4x O2

3. Gas Pressure
Pressure is defined as the force exerted per unit of area…for gas pressure, this pressure is exerted by a gas, for air pressure, it is exerted by the atmosphere…
Think of a column of air 1 inch by 1 inch from the ground up to space…that column would weigh 14.7 pounds per square inch… also
14.7 p.s.i=760 mmHg=101.3 kPa=760 Torr.
Let’s look at these units a little closer…

4. Inches or mm of Mercury
A mercury-filled glass tube, with a vacuum in the top is inverted into a dish of mercury…the height of the column is measured to measure the atomospheric pressure… inches of mercury=1atm=760mmHg=760 millibars.
This device is called a barometer.

5. More on Units of Pressure
The SI unit of pressure is the Pascal.
1 atm=760 mmHg=29.93 inchesHg=14.7 p.s.i.
760 mmHg=760 Torr.=760 millibars
Like a barometer measures the atmospheric pressure, a manometer measures a sealed container’s pressure.

6. Math with Pressure Units
Convert pressure units using dimensional analysis.
Example… Convert 788 mmHg to atm…
Example2… Convert 788 mmHg to kPa….

7. Answers UK: atm K: 788 mmHg 788 mmHg x 1atm = 1.036842 atm 1 760 mmHg
Round to 3 sd… atm
UK: kPa
788 mmHg x kPa = kPa
Round to 3 sd…. 105 kPa

8. Dalton’s Law
Dalton’s law of partial pressures states that the partial pressures in a space or container add up to the total pressure of the space or container.
PTOTAL= P1+P2…..+PFINAL
Example1 CO2 pressure = .55 atm O2 pressure = .75 atm
What is the total pressure of these two gases in a sealed container?
.55 atm atm = 1.3 atm

9. 12-2 Intramolecular Attractions
+/- attraction between a cation and anion make ionic bonds some of the strongest.
Covalent bonds are made by sharing of electrons.
Metallic bonds are caused by the free-moving sea of electrons (mobile electrons) which hold the metal + ions together.

10. 12-2 Forces of Attraction Between Molecules
The attractions between molecules are called intermolecular attractions.
For molecular compounds, these attractions are ….
Dispersion forces….electron motion causes attraction
Dipole attractions….+/- attraction of molecules
Hydrogen bonding…+/- attraction of H+ and an anion.
Ionic compounds are solids at room temperature because they have strong +/- attractions.

11. Properties of Compounds and Metals
Most molecular compounds are gas or liquid, and have a low melting/boiling point.
Ionic compounds have very high melting/boiling points.
Metals have high melting/boiling points.