Overview of Physical Properties of Gases. Gas Pressure

Transcription

1 Overview of Physical Properties of Gases! volume changes with pressure! volume changes with temperature! completely miscible! low density gases: < 2 g/l liquids and solids: 1000 g/l Gas Pressure force in all directions

2 Gas Pressure Pressure = force area Pascal, the SI standard F (N) P (Pa) = S (m2) kg! 9.81m/s2 = Pa 1 m2 at 0 oc, at see level Gas Pressure Pressure = force area F (N) P (Pa) = S (m2) 1 atm = Pa at 0 oc, at see level

3 >500 km of air Gas Pressure kg! 9.81m/s2 = Pa 1 m2 For mercury: 760 mm 1 atm = Pa = 760 mmhg (torr) For water: ~ 34 feet Ideal Gas Laws complete description of a sample of gas:! volume (V)! pressure (P)! temperature (T)! amount (n)

4 Ideal Gas Laws PV = nrt Ideal Gas Laws PV = nrt PV =R nt

5 Ideal Gas Laws PV =R nt R = 8.31 J mol-1 K-1 universal gas constant R = atm L mol-1 K-1 Ideal Gas Laws PV =R nt universal gas constant R = atm L mol-1 K-1

6 Ideal Gas Laws PV nt = R Ideal Gas Laws PV nt = R fixed n and T PV = constant Boyle s law

7 Ideal Gas Laws PV nt = R fixed n and T PV = constant Boyle s law V T fixed n and P = constant Charles law fixed n and T Ideal Gas Laws PV nt = R fixed n and P fixed P and T PV = constant Boyle s law V T = constant Charles law V n = constant Avogadro s law

8 Boyle s Law at fixed n and T P 1 V 1 = P 2 V 2 Charles Law at fixed n and P V 1 V = 2 T 1 T 2

9 Avogadro s Law at fixed P and T V 1 V = 2 n 1 n 2 Gas at Standard Conditions Standard conditions are standard temperature and pressure STP: 0 o C and 1 atm (760 torr) Volume of 1 mol of gas is 22.4 L

10 Ideal Gas molecules have mass, but no volume no attraction or repulsion between molecules move in straight lines between collisions no loss of energy during collisions, only transfer Molar Mass and Density PV = nrt and n = m M Molar mass: Density: M = d = mrt PV MP RT

11 Partial Pressure of Gases P total = P 1 + P 2 + P 3 + partial pressure is proportional to mole fraction that is, P 1 n = 1 P total n total P 1 = n 1 n total! P total Sample Problem 5.9 A small piece of zinc reacts with HCl to form H 2, which is collected over water at 16 o C into a large flask. The total pressure is adjusted to barometric pressure (752 torr), and the volume is 1495 ml. Calculate the partial pressure and mass of H 2. (P H2O at 16 o C is 13.6 torr).

12 Gas Laws and Stoichiometry P, V, T of gas A ideal gas law Amount (mol) of gas A molar ratio from balanced equation Amount (mol) of gas B ideal gas law P, V, T of gas B Sample Problem 5.10 Ammonia and hydrogen chloride gases react to form solid ammonium chloride. A 10.0 L flask contains ammonia at atm and 22 o C, and 155 ml of hydrogen chloride at 7.50 atm and 271 K is introduced. After the reaction occurs and the temperature returns to 22 o C, what is the pressure inside the flask?

13 Kinetic-Molecular Theory molecules have mass, but no volume no attraction or repulsion between molecules move in straight lines between collisions no loss of energy during collisions, only transfer Kinetic-Molecular Theory molecules have mass, but no volume no attraction or repulsion between molecules move in straight lines between collisions no loss of energy during collisions, only transfer The Meaning of Temperature Temperature is proportional to the average kinetic energy of molecular motion: E k = 3 2 R N A T

14 Kinetic-Molecular Theory Kinetic-Molecular Theory Nitrogen, N 2 : Diffusion Average molecular speed at 20 o C and 1 atm 0.47 km/s or 1100 mph Collision Frequency 7.1!10 9 collisions/s

15 Real Gases Deviation from ideal behavior are due to: 1. Intermolecular attractions 2. Molecular volume Real Gases

16 Real Gases: van der Waals equation P + n2 a V 2 b and a are (V - nb) = nrt van der Waals constants unique for each gas determined experimentally Practice Problems At 1400 mmhg and 13 o C, a diver inhales a 208 ml bubble of air that is 77% on N 2, 17% of O 2, and 6.0% of CO 2 by volume. (a) How many ml would the volume of the bubble be if it were exhaled at the surface at 1 atm and 298 K? (b) How many moles of N 2 are in the bubble?

17 Practice Problems An environmental engineer submits a sample of air contaminated with sulfur dioxide to the lab analysis. To a 500. ml sample at 700 torr and 38 o C, she adds ml of M aqueous iodine, which reacts as follows: SO 2 + I 2 + H 2 O " HSO I - + H + The unreacted I 2 is titrated with ml of M of sodium thiosulfate: I 2 + S 2 O 3 2- " I - + S 4 O 6 2- What is the volume % of SO 2 in the air sample? Hg Practice Problems