1. Gases & Atmospheric Chemistry Unit 5

2. States of Matter StateProperties Solid Definite shape and volume Are virtually incompressible Do not flow easily Liquid Assume the shape of the container but have a definite volume Are virtually incompressible Flow readily Gas Assume the shape and volume of the container Are highly compressible Flow readily

3. Solid, Liquid & Gas

4. Forces Holding Solids Together  The forces that are holding a solid together are very strong  Forces:  Ionic  Covalent  Some intermolecular forces in some substances

5. Forces Holding Solids Together Explains why solids:  Have a definite shape  Strong bonds holding molecules together (rigid)  Do not flow readily  In order to be able to flow particles have to slip past one another, strong bonds do not allow this  Cannot be compressed  Strong bonds mean that there are few empty spaces between the particles

6. Forces Holding Liquids Together  The forces that are holding a liquid together are not as strong as ionic or covalent bonds  Forces: intermolecular  Bonds hold molecules closely together but do not lock them into place  Liquids can spread out and take the shape of the container while keeping a constant volume

7.  Because gases have NO definite shape or volume there appears to be an absence of forces between the molecules in a gas  No limit to the diffusion of gas molecules into the atmosphere (a very large container) Gases – Lack of Forces

8. The Kinetic Molecular Theory  Kinetic Molecular Theory = the idea that all substances contain particles that are in constant, random motion  Particles are continually moving & colliding Explains: 1. Diffusion 2. Evaporation

9. Diffusion  Example: food colouring is added to water will slowly spread out  Explanation from Kinetic Molecular Theory: molecules of food colouring and molecules of water are moving and colliding with each other which causes them to mix

10. Evaporation  Example: water in an open container slowly decreases as some of the water evaporates  Explanation from Kinetic Molecular Theory : some water molecules in the open container obtain sufficient energy from collision to escape from the liquid

11. 3 Types of Motion  A particle an exhibit 3 type of motion: 1. Vibrational = back-and-forth motion of atoms within a molecule 2. Rotational = spinning 3. Translational = straight line

12. 3 Types of Motion

13. Motion in Relation to State  Solid – mainly vibration due to restriction of the strong bonds  Particles stay together in a relatively ordered state  Liquid – some of all 3 types of motion  Less orderly state than solid  Gas – rotate and vibrate but translational (straight-line) motion is the most significant  Most disordered state with no organization

15. Properties of Gases 1. Gases are compressible: When pressure is increased, the volume of a gas decreases. When pressure is decreased, the volume of a gas increases. The volume of a liquid and a solid remain constant during changes in temperature because their particles cannot move independently of one another like the gas particles can. 2. Gases expand as the temperature increases (much more than water and solid). 3. Gases have very low viscosity (they flow fast). 4. Gases have much lower densities than solids or liquids. 5. ALL Gases are miscible (some liquids are miscible yet some are immiscible).

16. Earth’s Leaky Atmosphere?  Many of the gases that make up Earth’s atmosphere and those of the other planets are slowly leaking into space.  Hot gases, especially light ones, evaporate away  chemical reactions and particle collisions eject atoms and molecules  and asteroids and comets occasionally blast out chunks of atmosphere

17. The Atmosphere

18. Measurement of Gas Pressure  Pressure = force exerted on an object per unit of surface area  Unit = Pa (pascal)  Atmospheric Pressure = the force per unit area exerted by air on all objects  Standard Atmospheric Pressure :  101.3 kPa or 760 mm Hg or 760 torr  one standard atmosphere (1atm)

19. Units of Pressure Unit of pressureSymbolInstruments that use the unit 1)Millimetres of Mercury: mm of Hg. mmHgBlood pressure meters 2) 1 TorrtorrVacuum pumps 3) Pascal (Pa) the SI unit of pressure. 1 kPa = 1000 Pa PaPressure sensors in pipelines 4) Bars: 1 barbarPressure sensors in scooba gear 5) Atmospheres (atm)atmGas compressors 6) Pounds per square inchPsiHydraulic pumps Conversion: 1 atm = 760 mm of Hg = 101.325 kPa = 1.01325 bar = 760 torr = 14.7 psi

20. 20 Pressure Conversions A. What is 475 mm Hg expressed in atm? 760 mm Hg = 1 atm 475 mm Hg = x x = 475/760 = 0.625 atm B. The pressure of a tire is measured as 10 kPa. What is this pressure in mm Hg?

21. 21 Pressure Conversions A. What is 2 atm expressed in torr?

22. STP & SATP  STP = Standard Temperature & Pressure  Exactly 0°C (273K)  1atm or101.325kPa  SATP = Standard Ambient Temperature and Pressure  exactly 25°C (298K)  100kPa

23. Gases Moving  Gases naturally move from areas of high pressure to low pressure, because there is empty space to move into  Examples of Spray Cans: whipped cream, hair spray, paint  a propellant forces the product out

24. Gas Law – Boyle’s Law Relationship: Pressure & Volume  As pressure on a gas increases, the volume of the gas decreases

25. Pressure and Volume Relationship  As pressure increases volume decreases

26. Gas Law – Boyle’s Law Relationship: Pressure & Volume  Boyle’s Law = as the pressure on a gas increase, the volume of the gas decreases proportionally p 1 v 1 = p 2 v 2  Provided that the temperature and amount of gas are constant  The volume and pressure of a gas are inversely proportional Graphically:P  1(inverse relationship) V Robert Boyle (1627-1691). Son of Early of Cork, Ireland.

28. Boyle’s Law Sample Problems: 1. A 350 mL sample of air at 125 kPa is reduced to a volume of 250 mL. Calculate the new pressure. (ans: 180 kPa) 2. A 55 mL sample of helium at 525 torr is compressed to a certain volume at 2.5 atm. What is the new volume, in litres? (ans: 0.015 L)