1. Gases and Laws – Unit 2 Version
Both the ideal and the real

2. Gases – the general Gases expand to fill any container.
random motion, no attraction
Gases are fluids (like liquids).
no attraction
Gases have very low densities.
no volume = lots of empty space

3. More generalities… Gases can be compressed.
no volume = lots of empty space
Gases undergo diffusion & effusion.
random motion

4. Gases – The ideal (KMT) Particles in an ideal gas… have no volume.
have elastic collisions.
are in constant, random, straight- line motion.
don’t attract or repel each other.
have an avg. KE directly related to Kelvin temperature.

5. Gases – Reality check Particles in a REAL gas…
Gas behavior is most ideal…
at low pressures
at high temperatures
in nonpolar atoms/molecules
Particles in a REAL gas…
have their own volume
attract each other

6. Units of measurement - Temperature
Always use absolute temperature (Kelvin) when working with gases.

7. Units of measurement - pressure
KEY UNITS AT SEA LEVEL
kPa (kilopascal)
1 atm
760 mm Hg
760 torr
14.7 psi
Pressure is measured with tools like the barometer (atmospheric pressure) and the manometer (contained gas pressure).

8. Standard Temperature & Pressure
The standard - stp
Standard Temperature & Pressure
0°C K
1 atm kPa

9. How to measure gas pressure
U-Shaped Manometer
A liquid is placed in the tube, usually a responsive liquid like mercury that is stable under pressure. One end of the U-tube is then filled with the gas to be measured, usually pumped in so the tube can be sealed behind it. The other end is left open for a natural pressure level. The atmospheric pressure pushes down on the liquid, forcing it down and into the closed end of the tube. The gas trapped in the sealed end also pushes down, forcing the liquid back to the other side. Then a measurement is taken to see how far the liquid in the sealed end has been pushed either below the point of the liquid in the open end or above it. If the liquid is level, straight across in both tubes, then the gas is equal to outside air pressure. If the liquid rises above this level in the sealed end, then the air's pressure is heavier than the gas. If the gas is heavier than the air, it will push the liquid in the sealed end below the equal point.

10. PV = k The laws – boyle’s P1V1 = P2V2
The pressure and volume of a gas are inversely related
at constant mass & temp
PV = k
P1V1 = P2V2

11. The laws – Charles’ V1 / T1 = V2 / T2
The volume and absolute temperature (K) of a gas are directly related
at constant mass & pressure
V1 / T1 = V2 / T2

12. The laws – Avogadro’s principle
Equal volumes of gases contain equal numbers of moles
at constant temp & pressure
true for any gas
V1 / n1 = V2 / n2

13. The laws – gay-lussac
At constant volume, pressure and absolute temperature are directly related.

14. The laws – Dalton’s
The total pressure of a mixture of gases equals the sum of the partial pressures of the individual gases.