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Chapter 20

CHEM 1C Chapter Notes - Chapter 20: Nernst Equation, Hydride, Sodium Chloride


Department
Chemistry
Course Code
CHEM 1C
Professor
Eric Potma
Chapter
20

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Chapter 20: Electrochemistry
20.1 Lightning and Batteries
- electrons flow away from a negative charge and towards a positive charge
20.2 Balancing Oxidation-Reduction Equations
- oxidation is the loss of electrons, reduction is the gain of electrons
- Oxidation corresponds to an increase in oxidation state, and reduction corresponds to a decrease in
oxidation state
- redox reactions must balance both number of each atom and charge
- aqueous redox balanced through half-reaction method of balancing, two reactions: 1) oxidation 2) reduction
20.3 Voltaic (or Galvanic) Cells: Generating Electricity from Spontaneous Chemical Reactions
- Electrical current = the flow of electric charge
-Electrochemical cell = a device that generates electricity through redox reactions
-voltaic (or galvanic) cell = produces electrical current from a spontaneous chemical reaction.
- electrolytic cell = consumes electrical current to drive a nonspontaneous chemical reaction.
- half-cell = one of two electrodes in a galvanic cell, two half-cells make an oxidizing-reducing couple
- electrodes = conductive surfaces through which electrons can enter or leave the half-cells
- zinc has a higher potential so zinc has greater tendency to ionize than copper
- electrons spontaneously flow from zinc electrode to copper electrode
- equilibrium for zinc shifts to the right, while equilibrium for copper shifts to the left
- the rate of electrons flowing through a wire is analogous to the rate of water moving through a stream
- potential difference = the measure of the difference in potential energy (usually in joules) per unit charge
(coulombs)
- electromotive force (emf) = is potential difference because it gives rise to a force that moves electrons
- cell potential (Ecell) (cell emf) = potential difference between two electrodes in voltaic cell
- standard cell potential (E°cell) (standard emf) = cell potential as reactants & products are in standard states
- negative cell potential indicates that the forward reaction is not spontaneous
-anode = electrode where oxidation occurs
- cathode = electrode where reduction occurs
- salt bridge = pathway by which counterions can flow between half-cells, without solutions mixing
- The negative ions within the salt bridge flow to neutralize the accumulation of positive charge at the anode,
and the positive ions flow to neutralize the accumulation of negative charge of the cathode
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