Properties of Gases

1. Properties of Gases

2. Gases • We use gases in our everyday live • Fridges, fuel, deep sea diving (ok not everyday) • Force due to gas is called pressure • SI unit Pa = 1 Newton/metre2 • Atmospheric pressure is the amount of pressure exerted by air – at sea level about 101 kPa.

3. Units Pg. 149

4. Relationship between Pressure and Volume • We can see that if we increase the volume the pressure decreases, and if we decrease the volume the pressure increases. • Pressure and volume have an inverse relationship • All other conditions are left the same, temperature, amount of substance

5. Boyle’s Law P1V1 = P2V2 • As the pressure on a gas increases, the volume of the gas decreases proportionally, provided that the temperature and chemical amount of gas remain constant.

6. Relationship between Temperature and Volume • Jacques Charles observed that there is a relationship between temperature and volume when doing experiments using hot air balloons. • Units of temperature (˚C) or kelvin (k). • Absolute zero is 0 k nothing can be colder.

7. Cooling of a Gas

8. Charles’ Law V1 / T1= V2/ T2 • As the temperature of a gas increases, the volumes increases proportionally, provided that the pressure and chemical amount of gas remain constant • This needs to be done in kelvin • T (K) = t (˚C) + 273

9. Combined Gas Law • Boyle’s Law PV = constant • Charles’ Law V/T = constant • We are able to combine both to give P= constant

10. Summary P1V1 = P2V2 • STP: 0 ˚ C and 101.325 kPa • SATP: 25 ˚ C and 100. kPa • 101.325 kPa = 1 atm = 760 mm Hg • T (K) = t (˚ C) + 273 V1 / T1= V2/ T2 P= constant

11. Properties of Gases • Kinetic molecular theory explains a lot about the properties of gases • Gases are compressible - the distance between the molecules • Gas pressure – the amount of collisions that occur • Boyle’s Law • Charles’ Law

12. Molecular motion

13. Combining volumes • Law of combining gases • when measured at the same temperature and pressure, volumes of gaseous reactant and products of chemical reactions are always in simple ratios of whole numbers • Avogadro’s Theory • Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules

14. Example • H2 + Cl2 -> 2HCl • Since the ratio is 1:1:2 then if 1.0 L of hydrogen combined with 1.0 L of Chlorine it would give 2.0 L of hydrogen chloride. • These ratios hold true for coefficients, chemical amounts, and volumes

15. Molar Volume of Gases • The volume that one mole occupies at a specified temperature and pressure • Combining the laws we have learnt previously • Given the symbol Vm • V = nVm OR n = V/Vm • The relationship of chemical amount (n), volume (V) and molar volume (Vm) • At STP one mole has a volume of 22.4 L • At SATP one mole has a volume of 24.8 L

16. The Ideal Gas Law • Law based on how gases will interact within a system. • Hypothetically all gas follow this law • Need to make a few assumptions from the real world

17. PG. 172

18. Ideal Gas Law • If we recall Boyle’s Law • Charles’ Law • Avogadro’s theory • Can combine all these to give: • - constant • -universal gas constant

19. Application • http://jersey.uoregon.edu/Piston/

20. Partial Pressure • The pressure inside a closed container is maybe up of the pressure of each of the gases would have in the same volume contained within it. • P = P1 + P2 + P3 + … • Example: • H2(g)+ Cl2(g)-> 2HCl(g) • P = PH2 + PCl2 + PHCl