1. Chapter 5 Gases Department of Chemistry and Biochemistry Seton Hall University

2. 2 Gas Laws Theories of gas behavior are based on motions of gas particles –particles of gas move freely through volume of enclosure –collisions occur between gas particles and walls of enclosure –frequency of gas collisions depend on the number of particles per unit volume (density=n/V)

3. 3 Molecular speeds and energy Speeds of particles are related to the energies of the particles (KE a function of temperature) At a given temperature, all particles have the same molecular kinetic energy distribution (see figure 5.4)

4. 4 Connections between speed and temperature

5. 5 Speed Note - rms speed is speed from taking the square root of the average (mean) value of u 2 Things that depend on speed –Effusion - movement of molecules escaping into a vacuum –Diffusion - movement of one type of molecule through molecules of another type –see Figure 5.6, 5.7

6. 6 Pressure collective effect of molecular collisions force per unit area units of pressure –1 Pa = 1 N/m 2 –1 atm = 1.01325  10 5 Pa –1 atm = 760 torr = 760 mmHg

7. 7 Ideal gas assumptions volume occupied by molecules is negligible compared to volume of the container energies generated by forces between molecules are negligible compared to molecular kinetic energies

8. 8 Molar mass of gases

9. 9 Gas Mixtures - Dalton’s Law of Partial Pressure

10. 10 Lower gas concentrations 1 ppm = 1 molecule out of 10 6 1 ppb = 1 molecule out of 10 9 X a, ppm, ppb all ratios of moles of a given gas to the total moles of gas ppm = 10 6 X ppb = 10 9 X

11. 11 Vapor pressure Evaporation - process by which molecules move from the liquid phase to the gas phase (below bp) Vapor - gas that results from evaporation Note, puddles of water disappear because equilibrium is never established

12. 12 Relative humidity The atmosphere normally contains less water than is possible at a given temperature e. g. p water <vp water Since vp is T dependent, dew and fog form when T drops such that vp water <p water