Chapter 10. Physical Characteristics of Gases

Transcription

1 Chapter 10 Physical Characteristics of Gases

2 Kinetic Molecular Theory An understanding of the behavior of atoms that make up matter Ideal gas: an imaginary gas that perfectly fits all assumptions of the KMT Based on five basic assumptions Gases consist of large numbers of tiny particles that are far apart relative to their size

3 Collisions between gas particles and between particles and the container walls are elastic collisions (there is no loss in energy) Gas particles are in constant, rapid, random motion. They contain kinetic energy (energy of motion). There are no forces of attraction or repulsion between gas particles. The average kinetic energy of gas particles depends on the temperature of the gas. KE = ½ mv 2

4 Expansion Gases do not have a definite shape or volume Will expand to fill container A gas in a 1 liter container is poured into a 2 liter container, it now occupies 2 liters

5 Fluidity Attractive forces are insignificant so gas particles slide easily past each other Because liquids and gases flow, they are referred to as fluids

6 Low Density The density of gases are 1/1000 the density of liquids or solids

7 Compressibility Gases can be compressed due the amount of space between particles Can usually be compressed to 100 times unpressurized conditions

8 Diffusion and Effusion Gases will spread out and mix with one another Diffusion is the spontaneous mixing of the particles of two substances caused by their random motion. The speed, diameter, and attractive force between particles determines their rate of diffusion Effusion is the rate at which a pressurized gas will travel through a small opening; smaller mass moves quicker

9 Real Gases Real gases are ones that do not behave like ideal gases due to their conditions At very high pressures or very low temperatures the KMT cannot be held to as some of the assumptions fall apart

10 Pressure The force per unit area on a surface Symbolized with a P Pressure = force / area Force is measured in Newtons and area is measured in m 2 One atmosphere of pressure is N for every m 2

11 Measuring Pressure Barometer is used to measure atmospheric pressure Evangelista Torricelli in the early 1600 s Used an inverted tube filled with mercury and placed it into a pan of mercury The level in the tube fluctuated with varying pressure At sea level the height of mercury is 760 mm

12 Units of Pressure 1.00 atm (atmosphere) 101,325 Pa (Pascal. N/m 2 ) kpa 760 mm Hg 760 torr

13 Convert 125 kpa to atm.

14 Convert 1.35 atm to mm Hg.

15 Temperature Conversions F C C = (5/9)( F 32) C K K = C Standard Temperature and Pressure (STP) 1.00 atm and 0 C

16 Convert 32 C to K.

17 Convert -194C to K.

18 Boyle s Law The pressure and volume of a gas are inversely proportional to each other P 1 V 1 = P 2 V 2 As you increase the pressure on a gas you decrease the volume

19 How much space will a 375 ml gas at 1.25 atm occupy at 113 kpa?

20 At what pressure will a 375 ml gas at 1.25 atm occupy 525 ml?

21 Charles Law The temperature and volume of a gas are directly proportional to each other V 1 /T 1 = V 2 /T 2 As you increase the temperature on a gas you increase the volume The temperatures must be in Kelvin

22 How much space will a 375 ml gas at 27.0 C occupy at 103 C?

23 At what temperature will a 375 ml gas at -105 C occupy 525 ml?

24 Gay Lussac s Law The temperature and pressure of a gas are directly proportional to each other P 1 /T 1 = P 2 /T 2 As you increase the pressure on a gas you increase the temperature The temperatures must be in Kelvin

25 At what temperature will a gas at 675 mm Hg and 27.0 C have a pressure of 1.43 atm?

26 Combined Gas Law The combination of the three previous laws into one useful equation P 1 V 1 /T 1 = P 2 V 2 /T 2 Through cross-multiplication, a more useful form is P 1 V 1 T 2 = P 2 V 2 T 1

27 What volume would 500. ml of gas at 835 mm Hg and 22.0 C occupy at STP?

28 Dalton s Law of Partial Pressures The total amount of pressure in a container is equal to the sum of the individual pressures of the gasses P tot = P 1 + P 2 + If a gas is collected over water you must subtract out the partial pressure caused by the water vapor at that temperature Chart found in appendix

29 325 ml of hydrogen are collected over water at 20.0 C and 1.15 atm. What volume will the dry gas occupy at STP?