Chapter 18

Question 1

electrochemical cell

Answer 1

• an apparatus that converts chemical energy into electrical work or electrical work into chemical energy
• electrodes provide pathways through which the electrons produced and consumed in the two half-reactions flow to and from an external circuit

Question 2

anode

Answer 2

• an electrode at which an oxidation half-reaction (loss of electrons) takes place

Question 3

cathode

Answer 3

• an electrode at which a reduction half-reaction (gain of electrons) takes place.

Question 4

voltaic cell

Answer 4

• an electrochemical cell in which chemical energy is transformed into electrical work by a spontaneous cell reaction
• chemical rxns inside cell pump e- from anode to cathode

Question 5

electrolysis

Answer 5

• a process in which electrical energy is used to drive a nonspontaneous chemical reaction

Question 6

electrolytic cell

Answer 6

• a device in which an external source of electrical energy does work on a chemical system, turning reactant(s) into higher-energy product(s)
• electrons are pumped into the cathodes (making them the negative electrodes) and flow out the anodes (making them the positive electrodes)
• voltaic cells become electrolytic cells when the products of a voltaic reaction become the reactants in the electrolytic reaction used to “recharge” a battery

Question 7

standard reduction potential(E^o)

Answer 7

• the potential of a reduction half-reaction in which all reactants and products are in their standard states at 25°C
  
  • ie conc of all dissolved substances = 1M and pressure of all gases = 1atm
• bigger E^o=greater probability that reduction half-rxn will couple w/ oxidation half-rxn to produce a spontaneous redox rxn

Question 8

standard cell potential (E^o_cell)

Answer 8

• a measure of how forcefully an electrochemical cell in which all reactants and products are in their standard states can pump electrons through an external circuit
• how forcefully the cell can pump electrons out from their anodes, through external circuits, and into their cathodes
• larger diff btwn standard reduction potentals, larger E^o_cell can be built from them
• E^o_cell >0 for spontaneous cell rxns

Question 9

Faraday constant(F)

Answer 9

• the magnitude of electrical charge in 1 mole of electrons. Its value to three significant figures is 9.65 x 10⁴ C/mol e-

Question 10

standard hydrogen elctrode(SHE)

Answer 10

• a reference electrode based on the half-reaction 2 H+(aq) + 2e- ⇒ H2(g) that produces a standard electrode potential of 0.000 V
• consists of a platinum electrode in contact with a solution of a strong acid ([H1] = 1.00 M) and H(g) at 1.00 atm
  
  • platinum is not change by electrode rxn, it is just a chemically inert conveyor of e-

Question 11

Nernst equation

Answer 11

• an equation relating the potential of a cell (or half-cell) reaction to its standard potential (E°) and to the concentrations of its reactants and products

Question 12

cell potential(E_cell)

Answer 12

• the force with which an electrochemical cell can pump electrons through an external circuit
• measuring the potential of an electrochemical reaction allows us to calculate equilibrium constant values that
  may be too large or too small to determine from the equilibrium concentrations of reactants and products

Question 13

corrosion

Answer 13

• the deterioration of metals due to spontaneous electrochemical(oxidation) reactions
• Factors that promote corrosion:
  
  • presence of water
  • presence of electrolytes: electrolytes caryr electrical current btwn anodes and cathodes and facilitate cell rxns
    
    • corrosion is more rapid in seawater than freshwater
  • contact btwn dissimilar metals
    
    • metalls corrode more quickly when in contact with other metals that are less likely to be oxidized(have higher reduction potentials)

Question 14

preventing corrosion

Answer 14

1. protective coatings, including paint and chemical or electrochemical modification of metal surfaces to make them less reactiv
2. chemically bonding metal oxide coatings to metal surfaces
   
   1. bluing protects steel
3. attaching metal structures to objects made of more reactive metals(sacrificual anodes-usually zinc or aluminum/magnesium alloys)
   
   1. cathodic protection

Question 15

rechargeable batteries

Answer 15

• their spontaneous ΔG<0 cell rxns that convert chemical energy into electrical work can be forced to run in reverse
• recharging happens when external sources of electrical energy are converted into chem energy and drive nonspontaneous ΔG>0 reverse cell rxn, reforming reactants from products

Question 16

fuel cells

Answer 16

• a voltaic cell based on the oxidation of a continuously supplied fuel. The reaction is the equivalent of combustion, but chemical energy is converted directly into electrical energy
• never die unless fuel supply is cut off(open systems, although other batteries are closed)