CHEMISTRY II B. Chapter 10 & Chapter 12. Gases

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1 CHEMISTRY II B Chapter 10 & Chapter 12 Gases

2 Think to yourself! How do gas particles move/behavior?! What is the Kinetic Molecular Theory?! Gases are mostly empty space! Particles have no attractive or repulsive forces! Rapid constant random motion (really fast)! Elastic collision (no lost energy)

3 ! Nature abhors a vacuum Aristotle B.C.! We live submerged at the bottom of an ocean of air. Evangelista Torricelli 1644

4 1. Gases substances that exist in the gaseous phase under normal atmospheric conditions T = 25 o C p = 1 atm

5 HF, HCl, HBr, HI CO, CO 2 CH 4, NH 3, H 2 S, PH 3 NO, NO 2, N 2 O SO 2

6 Jupiter (H 2, He) Io (SO 2 )

7 Helix Nebula Orion Nebula

8 2. Pressure Ar molecules/atoms of gas are constantly in motion

9 Atmospheric Pressure

10 Standard Atmospheric Pressure 760 mm at 273 K at sea level barometer 1 atm = 760 mm Hg = 760 torr Torricelli Temperature = 0 o C pressure of the atmosphere is balanced by pressure exerted by mercury

11 Otto Von Guericke experiment In 1654 he designed a vacuum pump to withdraw air from vessels.

12 pressure = SI units p = F / A force area

13 pressure measurement manometer

14 Factors that influence gases 1. Pressure 2. Volume 3. Temperature 4. Number of particles (moles) p, V, T, n

15 Boyle s Law pressure volume relationship (temperature is constant) Boyle ( )

16 P 1/V

17 P 1/V p = constant/v P x V = constant P 1 x V 1 = constant P 2 x V 2 = constant P 1 x V 1 = P 2 x V 2

18 Sample Problems A gas at 750 mm Hg pressure and a volume of 2.56 L is compressed to a new pressure 820 mm Hg. Find the new volume A mole of STP is changed to a volume of 17.8 L. Find its new pressure in mm Hg

19 Charle s Law temperature volume relationship (pressure is constant)

20 V T

21 V T V = constant T V/T = constant V 1 / T 1 = constant V 2 / T 2 = constant V 1 / T 1 = V 2 / T 2

22 Gay-Luassac s Law! Pressure temperature relationship! Also known as Amonton s Law of Pressure-Temperature P T P 1 / T 1 = P 2 / T 2

23 Avogadro s Law amount volume relationship (pressure and temperature are constant) Avogadro ( )

24 n V n = constant x V n/v = constant n 1 / V 1 = constant n 2 / V 2 = constant n 1 / V 1 = n 2 / V 2

25 SUMMARY Boyle s Law P 1/V Charles s Law V T Gay-Luassac s Law P T Avogadro s Law n V

26 @ a constant pressure find the new volume if a gas with an initial volume of 2.8 a temperature of 22 o C if the gas is cooled to 0 o a constant volume of 1.0 L the pressure of a gas is o C. Find the new temperature if the pressure is increased to 4.0 atm.

27 1. IDEAL GAS EQUATION (1) p 1/V V 1/p (2) V T (3) n V V T V n V T n / p p V = const n T

28 p x V = const x n x T p x V = R x n x T p x V = n x R x T ideal gas equation

29 p V = n R T [R] = [p] [V] / [n] x [T] atm L mol K [R] = atm L / mol x K [R] = atm x L/ mol x K

30 [R] = atm x L / mol x K R = atm x L / mol x K ideal gas constant

31 2. MOLAR VOLUME What is the volume of 1 mol of a gas at K (0 o C) and 1 atm (760 mmhg)? standard temperature and pressure (STP) p V = n R T V = 22.4 L

32 p V = n R T V = 22.4 L V m = 22.4 L the molar volume at standard pressure and temperature is independent on the gas type

33 5. DALTON S LAW pure gases gas mixtures Dalton (1801) (atmospheres)

34 DALTON S LAW the total pressure of a gas mixture, p, is the sum of the pressures of the individual gases (partial pressures) at a constant temperature and volume p = p A + p B + p C +.

35 p V = n R T p A V = n A R T p B V = n B R T p A = n A R T / V p B = n B R T / V p = p A + p B p = (n A + n B ) R T / V p V = n R T

36 p V = (n A + n B ) R T p A = n A R T / V p A / p = n A /(n A + n B ) = x A mole fraction x < 1 p A = x A p

37 2 KClO3 2 KCl + 3 O2

38 1. Kinetic Molecular Theory of Gases macroscopic (gas cylinder) microscopic Maxwell ( ) (atoms/molecules) Boltzmann ( )

39 Kinetic Energy of Gases physical properties of gases can be described by motion of individual gas atoms/molecules each macroscopic and microscopic particle in motion holds an energy (kinetic energy)

40 Assumptions of the Kinetic Theory of Gases 1. gases are composed of atoms/molecules which are separated from each other by a distance l much more than their own diameter d d = m l = 10-3 m.. few m l molecules are mass points with negligible volume

41 2. gases are constantly in motion in random reactions and hold a kinetic energy gases collide and transfer energy (billiard ball model)

42 3. gases atoms/molecules do not exert forces on each other (absence of intermolecular interactions) F (inter) = 0 p (inter) = 0

43 Gas Diffusion

44 2. Distribution of Molecular Speeds Maxwell-Boltzmann distribution

45 3. Real Gases p V = n R T (n = 1) deviation of ideal gas law at high pressures p 90 atm