1. Chapter 6 - Gases

2. Physical Characteristics of Gases
Although gases have different chemical properties, gases have remarkably similar physical properties.
Gases always fill their containers (recall solids and liquids). No definite shape and volume
Gases are highly compressible: Volume decreases as pressure increases Volume increases as pressure decreases
Gases diffuse (move spontaneously throughout any available space).
Temperature affects either the volume or the pressure of a gas, or both.

3. Definition of a Gas
Therefore a definition for gas is: a substance that fills and assumes the shape of its container, diffuses rapidly, and mixes readily with other gases.

4. Three Gas Laws Pressure force of colliding particles per unit area
According to the KMT gases exert pressure due to the forces exerted by gas particles colliding with themselves and the sides of the container
SI unit for pressure is kilopascals - kPa

5. 1 kPa = 1000 N/ 1 m2
Atmospheric pressure – pressure exerted by air particles colliding
SATP – 100 kPa at 25 °C
STP – kPa at 0 °C

6. Boyle’s Law
As pressure on a gas increases the volume of the gas decreases proportionally as the temperature is held constant
P1V1 = P2V2

7. Charles Law
the volume of a gas increases proportionally as the temperature of the gas increases, if the pressure is held Constant
V1 = V2 T1 T2

8. Boyle’s Law – inverse relationship Charles Law – direct relationship

9. Kelvin Temperature Scale
Temperature - the average kinetic energy of the particles making up a substance
Kelvin Temp Scale: based of absolute zero — all kinetic motion stops
273°C = K °C = 273 K °C =303 K °C = 253 K
Formulas °C = K K= °C+273

10. Combined Gas Law This is when all variables (T,P, and V) are changing
P1V1 = P2V2
T T2

11. Avogadro’s Theory and Molar volume
The kinetic molecular theory is strongly supported by experimental evidence.
The K M theory explains why gases, unlike solids and liquids, are compressible.
The K M theory explains the concept of gas pressure.
The K M theory explains Boyle’s Law — Increase volume \ decrease pressure
The KM theory explains Charles’ Law Increase volume \ increase temperature

12. History Lesson 1808 – Joseph Guy – Lussac 1810 – AmadeoAvogadro
“Law of Combining Volumes”
When measuring at the same temp and pressure, volumes of gas reactants and products (in chemical reactions) are always in simple whole number ratios
1810 – AmadeoAvogadro
“Avogadro’s Theory”
Equal volumes of gases at the same temp and pressure have equal number of molecules

13. Molar Volume of Gases “new conversion ratio”
Avogadro says :
T1 = T2
P1 =P2
V1 = V2
Then # particles of gas 1 = # particles of gas 2
1 mol = 6.03 x particles
Lets put these two ideas together……

14. Therefore for all gases at a specific temp and pressure there must be a certain volume that contains exactly 1 mole of particles - molar volume
The two most standard temps and pressures are STP and SATP

15. Molar Volume When gases are at STP: When gases are at SATP:
1 mole of any gas = 22.4 L/mol
When gases are at SATP:
1 mole of any gas = 24.8 L/mol

16. Ideal Gas Equation
Ideal Gas — is a hypothetical gas that obeys all the gas laws perfectly under all conditions. It is composed of particles with no attraction to each other. (Real gas particles do have a tiny attraction)
The further apart the gas particles are, the faster they are moving the less attractive force they have and behave the most like ideal gases
The smaller the molecules the closer the gas resembles an ideal gas
We assume ideal gases always. .

17. Equation PV = nRT P = pressure (kPa)
V = volume (L) n = moles (mol) R = universal gas constant (8.31 kPa*L ) Mol * K T = temperature (K)
Sometimes the n must be converted to mass after the equation is completed. If this is necessary, use a conversion