HTML University

Science Dept.

Chemistry CHE 100 Notes
L. The Gas Laws

1. General Charachteristics
   1. Expansion to fill the container

   2. No shape

   3. No volume

   4. High Compressibility

   5. Low Density compared to Liquids and Solids

   6. Mixable or Miscible

2. Kinetic Theory: "Heat is nothing but the vibratory motion of molecules"
   ...Sir Isaac Newton
   1. Description of an "Ideal Gas"
      1. Molecules are very small in comparison to the total volume (and the distance between the molecules)

      2. No attractive forces between (among) molecules...actually there are!

      3. Molecules have rapid motion

      4. Molecular collisions are elastic

      5. KE_ave is proportional to T^o K

      6. N.B.Conditions above refer to an "Ideal Gas" and are approximations of real gases when real gases are under low to moderate Pressure and are under moderate to high Temperature. When the Temperature is low and the Pressure is high, real gases deviate from the "Ideal Gas."

3. Pressure
   1. Pressure = Force/unit Area, or in symbolic form, P = F/A

   2. Atmospheric Pressure was measured by Evangelista Torricelli (1608 to 1647) by using a Mercury (Hg) barometer

   3. One Atmospheric Pressure can be measured:
      1. As 14.7 psi or pounds/sq.in.

      2. As 760 mm Hg

      3. As 760 Torrs

      4. As 29.9 inches Hg

      5. As One Standard Atmosphere

      6. As 1013 millibars or 1.013 x 10⁵ pascals

   4. Atmospheric Pressure decreases with increasing altitude, about 25 torr per 1000'

   5. Atmospheric Pressure varies with climatic conditions

4. Boyles Law
   1. The variables are: P, V, n and T; with n in moles and T in^oK
      the nature of the molcule is of little consequence

   2. In Boyle's Law n and T are kept constant

   3. P varies inversely with V, that is P is proportional to 1/V

   4. P = k/V; rearranging the equation yields: PV = k

   5. P₁V₁ = k = P₂V₂

   6. P₁V₁ = P₂V₂

5. Charle's Law
   1. The variables are: P, V, n and T; with n in moles and T in^oK
      the nature of the molcule is of little consequence

   2. In Charle's Law n and P are kept constant

   3. V varies directly with T, that is V is proportional to T

   4. V = kT; rearranging the equation yields: V/T = k

   5. V₁/T₁ = k = V₂/T₂

   6. V₁/T₁ = V₂/T₂

6. Gay-Lussac's Law
   1. The variables are: P, V, n and T; with n in moles and T in^oK
      the nature of the molcule is of little consequence

   2. In Gay-Lussac's Law n and V are kept constant

   3. P varies directly with T, that is P is proportional to T

   4. P = kT; rearranging the equation yields: P/T = k

   5. P₁/T₁ = k = P₂/T₂

   6. P₁/T₁ = P₂/T₂

7. Avogadro's Law
   1. The variables are: P, V, n and T; with n in moles and T in^oK
      the nature of the molcule is of little consequence

   2. In Avogadro's Law P and T are kept constant

   3. V varies directly with n, that is V is proportional to n

   4. V = kn; rearranging the equation yields: V/n = k

   5. V₁/n₁ = k = V₂/n₂

   6. V₁/n₁ = V₂/n₂

   7. This will eventually be seen as the molar volume of a gas:
      One Mole of a gas will occupy 22.4 liters at STP (O^oC at One Standard Atmosphere)

8. The Ideal Gas Law
   1. PV = nRT

   2. Remember: n in moles and T in^oK

   3. P and V can be used with a variety of units, but the proper constant, R, must be chosen

   4. R can be calculated by using the molar volume of a gas
      1. (One Standard Atmosphere)(22.4 liters) = (One Mole)(R)(273.14^oK)

      2. Rearranging: [(One Standard Atmosphere)(22.4 liters)]/ [(One Mole)(273.14^oK)] = R

9. Dalton's Law of Partial Pressures
   1. P_T = P₁ + P₂ + P₃ + ... + P_n

   2. For Example: P_Air = P_N2 + P_O2 + ... + P_CO2 + P_H2O

   3. By Volume Dry Air = 100% = 78.1% N₂ + 20.9% O₂ + ... + 0.03% CO₂

   4. Therefore the Partial Pressures of Dry Air = One Standard Atmosphere = P_T = 0.781 N₂ + 0.209 O₂ + ... + 0.0003 CO₂

10. Neat Sites
    1. Important Links to Atmospheric Chemistry
    2. York Univ Center for Atmospheric Chemistry
    3. Atmospheric Chemistry
    4. Global Atmospheric Chemistry Group at Univ of NH
    5. NASA Laboratory for Atmospheres
    6. Glossary of Terms in Atmospheric Chemistry