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CHM 142 EXAM 4 questions and answers 100% complete solution 2024/2025
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CHM 142 EXAM 4 questions and answers 100% complete solution 2024/2025
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CHM 142 EXAM 4Electrons flow ______ one way in a redox reaction, from _____________ potential
energy.
spontaneously, high to low
Electricity
the movement of electric charge, carried by charge carriers (ions or electrons)
oxidation occurs at the
anode
reduction occurs at the
cathode
Voltaic Cells
use spontaneous oxidation-reduction reactions to convert chemical energy into
electrical energy
Electromotive force (emf) or cell potential (Ecell)
The potential difference between the anode and cathode in a cell
Cell potential is effected by
- the reactions that occur at the cathode and anode
- the concentrations of aqueous reactants and products
- The pressures for gaseous reactants and products
- The temperature
- Measured in volts (V)
- One volt is one joule per coulomb
Standard cell potential
the cell potential under standard conditions that occurs at the cathode and anode
SHE
Standard hydrogen electrode. 2H+ (aq) + 2e- --> H2 (g)
Easiest to reduce and strongest oxidizing agent
F2 (g)
Easiest to oxidize, strongest reducing agent
Li (s)
Gibbs free energy
measure of spontaneity
n
the number of electrons transferred in the redox reaction or the number of electrons
crossed out when adding the half reactions together.
not on equation sheet
E°=(RT/nF)lnK
Concentration cell
has the same substance at both electrodes, but possibly at different concentrations
Batteries
a portable, self-contained electrochemical power source that consists of one or more
voltaic cells
, Primary cells
not designated to be recharged when "dead"
Secondary cells
can be recharged
Electrolysis reactions
where electricity provides external assistance for reactions that would otherwise not
happen (non spontaneous reactions)
Lead-Acid Battery
A battery that runs on the oxidation of lead and the reduction of lead(IV) oxide in the
presence of sulfuric acid. Can provide enough power to start an engine.
Alkaline battery
most common primary battery. Non-rechargeable "AA" and "AAA" are usually of this
type.
Fuel Cell
a voltaic cell that uses conventional fuels, such as H2, CH4, or CH3OH as one reactant.
O2 is often another reactant make the equation look like a combustion reaction. These
are NOT batteries.
When a fuel is burned,
chemical energy can be converted to heat energy and then to electrical energy
Hydrogen gas
the easiest fuel to use in fuel cells, but it is hard to store and transport
Corrosion
a spontaneous redox reaction in which a metal is attached by some substance in the
environment and converted to an unwanted compound
Rusting requires
both oxygen gas and water
Rusting is accelerated by these factors
pH, presence of salts, contact with metals more difficult to oxidize than iron, and
physical stress on the iron
Corrosion prevention
Coating with paint or with another metal (galvanization)
Cathodic Protection
Protecting a metal by making it the cathode in an electrochemical reaction
Sacrificial anode
the metal that is oxidized while protecting the cathode
Protons
positive charge
electrons
negative charge
neutrons
neutral charge
Protons and neutrons have the _______ mass
same
Mass number (A)
the total number of protons and neutrons in a nucleus.
Atomic number (Z)
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