110_Fa11_LUZ-week9ST - Week 9 Real gases deviate from ideal behavior The 5 key postulates of KMT Straight-line motion in random directions

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Week 9: Lectures 25 – 27 Lecture 25: W 10/19 Lecture 26: F 10/21 Lecture 27: M 10/24 Reading: BLB Ch 18.1 – 18.4, 5.5, 11.3 – 11.6 Homework: BLB 18: 9, 11, 15, 29, 69; Supp 18: 1 – 3; BLB 11:33, 37, 39, 31, 43, 47, 50; Supp 11:5 - 13 Reminder: Angel Quiz 8 due on Thur 10/20 ALEKS Objective 9 due on Tue 10/25 Jensen Office Hour: 501 Chemistry Building Tuesdays & Thursdays, 10:30 – 11:30 am TA office hours, evening tutor sessions, guided study group info posted on Angel -> Help Available Exam 3: Monday Nov 7 6:30 – 7:45 pm Jensen Chem 110 Chap 10 Page: 2 Real gases deviate from ideal behavior The 5 key postulates of KMT ! Straight-line motion in random directions ! Molecules are small & have “no” volume compared to the total volume ! No intermolecular forces ! Elastic collisions ! Mean kinetic energy ! " T (in K) For a non-ideal gas (real gas) this is not true for two types of conditions: high P low T Reasons: Molecules (or atoms) have a finite size molecules occupy space Molecules have attractive forces these forces become stronger when they are close together
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Jensen Chem 110 Chap 10 Page: 3 Real Gases – Pressure For 1 mol of any ideal gas: PV/(RT) = 1 For 1 mol of different gases at same T & different P: At low P, the ideal-gas equation is valid: PV/(RT) = 1 In general, deviation from ideal behavior increases as P increases: At high P, attractive forces between molecules lead to the appearance of a smaller n PV/(RT) < 1 Example: CO 2 at 200 atm At very high P, finite molecular volume leads to repulsion and the appearance of a larger n PV/(RT) > 1 Example: CO 2 at 800 atm Low P PV/(RT) ~ 1 High P: PV/(RT) < 1 Very high P PV/(RT) > 1 Jensen Chem 110 Chap 10 Page: 4 Real Gases – Temperature For 1 mol of any ideal gas: PV/(RT) = 1 For 1 mol of N 2 gas at different T & different P At low T , molecules stick together: PV/(RT) ! 1 As temperature increases, molecules move faster, the behavior of real gases becomes more ideal.
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Chem 110 Chap 10 Page: 5 Summary Example: Under which conditions is Ar(g) most likely to approach ideal behavior? A. 10 atm and 100°C B. 1.0 atm and -200°C C. 0.10 atm and –100°C D. 20.0 atm and 100°C E. 0.10 atm and 200°C High P PV/RT < 1 Attractive forces lead to the appearance of a smaller n Very high P PV/RT > 1 Finite molecular volume leads to repulsion and the appearance of a larger n Low P PV/RT ! 1 Attractive forces and finite molecular volume have minimal impact As T # , real gas behavior becomes more ideal At high T, Kinetic energy overcomes attractive forces Jensen Chem 110 Chap 10 Page: 6 Correcting the Ideal Gas Law For any gas, we can measure P, V, T At higher P , measured P is too small due to attractive forces between molecules The amount of “missing” P is proportional to 1. size of attractive forces ( a ): 2. frequency of collisions: ( n 2 /V 2 ) To compensate , use: At higher P, measured V is too large due to finite molecular
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This note was uploaded on 01/18/2012 for the course CHEM 110 taught by Professor Hofmann,brucerob during the Fall '08 term at Pennsylvania State University, University Park.

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110_Fa11_LUZ-week9ST - Week 9 Real gases deviate from ideal behavior The 5 key postulates of KMT Straight-line motion in random directions

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