P total Water insoluble gaseous product bubbles through water into collection

P total water insoluble gaseous product bubbles

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P total Water-insoluble gaseous product bubbles through water into collection vessel 1 Collecting a Water-Insoluble Gas and Determining Its Pressure 2 KClO 3 (s) 2 KCl (s) + 3 O 2 (g)
Partial Pressure Example Oxygen, O 2 , is produced in the lab when KClO 3 is heated: 2 KClO 3 ( s ) à 2 KCl( s ) + 3 O2(A sample of KClO3is completely decomposed and all of the O2is collected over water. If the total gas pressure is 738 torr and the volume is 523 mL at 23 °C, how many grams of O2are collected? The vapor pressure of water is 21 torr at g )
Kinetic-Molecular Theory (a microscopic view of gas behavior) The gas laws are empirically determined descriptions of macroscopic or bulk properties of gases. Kinetic-Molecular (K-M) Theory describes microscopic (molecular) properties and explains gas behavior in terms of the gas particle motion (atoms or molecules). Example: Pressure of a gas (P) à
Assumptions of K-M Theory The gas particles in an ideal system: average KE α mv 2 α T
Molecular View of Boyle’s Law
Molecular View of Charles’ Law V
Speed Distribution with Temperature ( E kin ) avg = 3.40 kJ mol -1 ( E kin ) avg = 28.35 kJ mol -1 ( E kin ) avg = 15.88 kJ mol -1 •Not all particles have the same speed •There is a range of speeds described by a distribution (which depends on T )
0 2x10 2 4x10 2 6x10 2 8x10 2 10x10 2 Fraction of molecules with speed u u (m / s) u mp u avg u rms rms = root mean square for particles with E kin = (E kin ) avg u rms = 3R T M Note tail to higher speeds Speed Distribution No stationary particles
Differences between Definitions of Typical Speeds (1) mean or average speed (2) most probable speed (3) rms speed Example: assume five speeds: 2, 4, 4, 6 and 8 m/s -a discrete, as opposed to a continuous, distribution m/s 4.8 5 24 5 8 6 4 4 2 u avg = = + + + + = m/s 4.0 u mp = m/s 5.2 5 136 5 8 6 4 4 2 u 2 2 2 2 2 rms = = + + + + =
O 2 (32) N 2 (28) H 2 O (18) He (4) H 2 (2) Molecular speed at a given T Relative number of molecules with a given speed root-mean-square speed Consider gases at the same T but with different molar masses. A lighter gas has a higher u than a heavier gas. Relationship between Speed and Molar Mass But, all gases have the same ( E kin ) avg = ½ mu rms 2 u rms = 3R T M gas u rms (m s -1 ) O 2 482 N 2 515 H 2 O 643 He 1364 H 2 1928
Gas Movement in a System Diffusion (net path of gas) Effusion (through pinhole)
Graham s Law of Effusion The effusion rate of a gas is inversely proportional to the square root of its molar mass. ( T. Graham ) the effusion rate; r u rms 1 2 2 1 2 1 2 1 3RT/ 3RT/ u u r r M M M M = = = Explanation:

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