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One other unique and highly useful feature of red ox reactions …

One other unique and highly useful feature of red ox reactions …. The oxidation and reduction can be separated in space and you can still run the reaction as a `cell’ or ‘ battery’. Example: Cu-Mg cell. The complete redox reaction . Gains 2e -. Cu 2+ + Mg o  Cu o +Mg 2+.

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One other unique and highly useful feature of red ox reactions …

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  1. One other unique and highly useful feature of redox reactions… The oxidation and reduction can be separated in space and you can still run the reaction as a `cell’ or ‘battery’

  2. Example: Cu-Mg cell The complete redox reaction Gains 2e- Cu2++ Mgo Cuo +Mg2+ Loses 2e- Reduction half reaction: Cu2+ +2e- Cuo cathode Oxidation half reaction: MgoMg2+ +2e- anode Cu2++ Mgo Cuo +Mg2+

  3. The experimental set-up of (Mg|Mg2+ ||Cu2+ |Cu) cell LOAD Electron flow out of anode Mg0Mg2+ +2e- NaCl bridge Cl- Na+ anode cathode Cu2+ +2e-Cuo Oxidation Reduction

  4. Traditional demo • Potato clock

  5. Molecules all by themselves Our Chemistry Road trip so far… mostly individual, isolated molecular/atomic properties Now we take up the Chemistry of the Crowd Chapter 7:Gases (pp. 281-316) our first exploration of `aggregate’ behavior

  6. Pressure (P) concepts & measures in “Physics-speak “(see p 283-4) P = Force Area Physics speak P=newtons m2 Physics units =kg*m/s2 =kg m s2 m*m

  7. Pressure (P) concepts & measures in “Physics-speak“(see p 283-4)  1 kg = 1Pascal (Pa) m s2

  8. Some lowbrow cheminsights into Pressure • Getting hammered • Bed of nails

  9. Pressure expresses how much a (constant)impressed force is spread out… • MORE AREA, LOWER PRESSURE • LESS AREA, HIGHER PRESSURE

  10. Pressure in `lowbrow’ Chem speak: barometers ( see p 283) outer space Pressure =1 atmat sea level ~20 mile tall column of air in Earth’s atmosphere creates pressure we all feel Earth Edge of Earth’s atmosphere

  11. Pressure in `lowbrow’ Chem speak (continued): barometers ( see p 284) Evacuated space External atmospheric pressure, P P in mm Hg A Torricelli barometer Hg

  12. Atmosphere demonstrated the Italian Way (BIG time Torricelli Barometers) Lesson from 17th century picture Height of Hg columns is independent of cross-sectional areas of tubes Vat of mercury (Hg)

  13. in CHEMISTRY LAND Pressure units 1 atmosphere =760 mm Hg = 760 torr =29.92 inches Hg Other common measures of an atmosphere 1 atmosphere=10336 mm H2O =33.9 ft H2O = 20 miles of air = 15 pounds/in2 (psi)

  14. Pressure units in PHYSICS COUNTRY Physics speak 1 atm = 101.3 kPa Confusing Compromise 1 bar =100 kPa= 0.986 atm WE ARE GOING TO STICK WITH ATMOSPHERES (atm) IN THIS COURSE

  15. Empiricgas law derivations:the common sense way What variables do we follow when describing a gas ??? P, T, V, n n P Tup  ?? Vup => T, V vary Tdown ?? Vdown CHARLES’ LAW (p. 287-8) V V = bT V1 = T1 V2T2 T V1/T1= V2/T2

  16. Empiricgas law derivations:the common sense way (cont.) nT V down ?? Pup => P, V vary Vup ??  Pdown P BOYLE’S LAW (p. 285-6) P = k/V P1 = 1/V1 P21/V2 V P1V1=P2V2

  17. Empiricgas law derivations:the common sense way (cont.) n V Tup ?? Pup => T, P vary Tdown ?? Pdown P GAY-LUSSAC’S LAW (not in text) P = aT T in K T1= P1 T2P2 T P1/T1= P2/T2

  18. How Boyle, Gay-Lussac and Charles Laws are reflected in the Combined Gas Law (when n is constant) Conditions Gas Law Equation Name of Gas Law P1V1 = P2 V2 T1 T2 constant n Combined Gas Law constant n,P P1V1 = P2 V2 T1 T2 Charles’ Law (P1=P2) P1V1 = P2 V2 T1 T2 constant n, T Boyle’s Law (T1=T2) P1V1 = P2 V2 T1 T2 Gay-Lussac’s Law (V1=V2) constant n, V

  19. A sample of oxygen gas is expanded from 20 to 50 liters at constant temperature. The final pressure is 4 atm. What was the initial pressure ? P1=10 atm • A sample of gas at fixed volume is heated from 300 K • to 600 K. If the initial pressure is 5 atm, what is the • final pressure ? P2= 10 atm • The volume of a piston at fixed pressure changes as it is • cooled from 500 oC to 250oC. If the final volume is 6.76 L, • what is the initial volume ? V1=10 L

  20. 4. A child’s balloon originally occupies 5 liters at sea level (P=1 atm)and room temperature (300 K) . It is released and is allowed to riseto an altitude where the pressure is 0.25 atm and the temperatureis 150 K. What is the balloon’s new volume ? 10 L • Autoclaves are essentially pressure cookers. At 1 atm, • steam has a temperature of 100o C. Would you expect the • pressure to double if the autoclave to attains a steam • temperature of 200oC ? a) NO…must convert C K…ratio is not 200/100 What pressure do you actually expect to reach at 200 oC? 473.15 =1.73 atm 373.15

  21. Trickier Text problem 59 page 322 Stopcock closed 2.00 L H2 at 0.625 atm 1.00 L N2 at 0.200 atm Final P = ??? Stopcock open 0.483 atm

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