Today

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Today

• Balancing Redox reactions
• Properties of Gases
• Gas Laws

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WebAssign Assignment 4
Deleted one problem Balancing redox rxns in
basic solution. (this was problem 9 a -
e) See text Problem 62 (6th edition) Problem
58 (5th edition) Do this on your own.
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Balancing Redox Rxns

• 1. Assign Oxidation States
• 2. Write unbalanced half rxns
• a) Balance all atoms except O and H
• b) Include es lost or gained (determined from
  change in oxidation state)
• c) Balance charge (charge on ions and
  electrons)
• Acidic soln Add H to one side of eqtn
• Basic soln Add OH to one side of eqtn
• d) Balance oxygen atoms by adding H2O to one
  side of eqn

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Balancing Redox Rxns

• Multiply one or both half rxns by integer so that
  
• es gained es lost
• 4. Add half reactions

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Three States of MatterGas Liquid
Solid
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Measuring Air Pressure

• use a barometer
• column of mercury supported by air pressure
• force of the air on the surface of the mercury
  balanced by the pull of gravity on the column of
  mercury

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• At sea level P ?
• P 1 atm
• 1 atm 14.69 psi
• 1 atm 760 torr
• 1 atm 760 mm Hg (29.92 in Hg)
• 1 atm 1.01325 105 pascal (Pa)

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• Ideal Gas Law
• When a gas behaves according to this equation,
  then the gas is said to behave ideally.
• Is the air in this room an ideal gas?
• a) No b) Yes c) Not sure
• When P 1 atm (or close to 1 atm) most gases
  obay the ideal gas law equation.

PV nRT
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• When we cool a sample of gas we form a liquid. 
• As we cool the liquid we form a solid. 
• We can continue to cool the solid down to lower
  temperatures.
• What is the lowest possible temperature that we
  can cool any substance?

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Absolute Temperture

• N2 (l) boils at 197 oC
• N2 (s) freezes at 210 oC
• H2 (s) freezes at ?
• 259 oC
• He (s) freezes at ?
• 272 oC
• How low can we go?

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• From Experiment and Theory
• T 273.15 oC lowest possible T
• Define absolute temperature scale
• If T 100 oC, what is the temperature in Kelvin?

T (Kelvin) T (oC) 273.15