Electrochemical (Galvanic) Cell

• Electrons are produced at the anode and flow to the cathode. 

• Reduction occurs at the cathode; oxidation occurs at the anode -- TIP:  Red Cat (Reduction/Cathode)

• Reduction is gain of electrons; Oxidation is loss of electrons -- TIP:  OIL RIG (Oxidation is loss, Reduction is gain)

• Negative ions from the salt bridge flow to anode to neutralize positive ions being placed in solution. 

• Positive ions from salt bridge flow to cathode to replace positive ions being precipitated

• Increasing concentration around the cathode increases voltage. 

Collecting Gas Over Water - Experimental Set Up

• Possible experiments that use this set up: determine molar volume of a gas; determine the molar mass of a (unknown) gas

• Showing collecting a gas using water displacement. The tube on the right is originally filled completely with water at the start of the experiment. The collected gas is bubbled into the tube. 

• Usually there are graduated marks on the tube on the right in order to record the volume of gas collected. In order to note the volume, the water level in the tube must be the same as the tub - if not, a correction must be made because that indicates the pressure of gas in the tube is not equal to the atmospheric pressure (the pressure outside the tube). 

• The collected gas in the tube is assumed to be "wet" - containing water vapor as well - due to the fact the gas is collected over water. Must use Dalton's Law to account for what pressure is just due to the collected gas. 

  • • The partial pressure due to water can be well estimated from a chart, if temperature is known.

Potential Energy (PE) Diagram - Indicating Intermediates

• *One of the most common diagrams on the AP Exam**

• Catalysts are represented with peaks lower than that of the oriignal activated complex because they lower activation energy

• If products have a higher potential energy (PE) to start, the reaction is exothermic and if they have a higher PE in the end the reaction is endothermic. 

• The activation energy (Ea) is the vertical distance between the potential energy of the reactants and the potential energy of the activated complex. 

Maxwell-Boltzmann Distribution

• The x-axis is sometimes labeled “energy.” There is a direct correlation between molecular speed and kinetic energy. 

• The peak for the higher temperature molecules is lower and farther to the right (B in this example). 

• The peak for the higher temperature molecules has a greater area under the curve past the activation energy (not shown in this diagram). 

• Both curves always start at (0, 0)

• Both curves eventually flatten out at # of particles = 0

• Fraction of molecules is the same as # of particles.

and more ...

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