CHM 142 exam 4 Flashcards
the study of electricity and chemical reactions
electrochemistry
half- reactions
equations that only show oxidation or reduction alone
electrons are shown as— in oxidation
products
electrons are shown as — in reduction
reactants
What are the steps to balancing redox reactions?
- Balance any atoms that are not O or H
- Balance O by adding H20
- Add H to balance out any H added by the H2O
- Balance electrons (make sure charges are equal)
voltaic cell
a device that facilitates the transfer of electrons externally by a wire instead of directly through the reactants
loses mass over time, negative, where oxidation occurs, anions flow to this
anode
gains mass over time, positive, where reduction occurs, cations flow to this
cathode
what is the purpose of a salt bridge in a voltaic cell?
to keep the solutions neutral so electrons flow from anode to cathode
electrons flow—from the anode to the cathode
spontaneously
the potential difference between two electrodes of a voltaic cell
cell potential/emf/Ecell
Ecell=
Ecathode-Eanode
the more — a Ecell value is the more likely it is for — to occur
positive, reduction
what are four things that affect cell potential
- the reactions that occur at the electrodes
- concentration of products and reactants
- pressures of gaseous products or reactants
- temperature
Does changing the coefficents in a rxn equation change the cell potential?
No
if the value of Ecell is negative the rxn is —
nonspontaneous
If the value of Ecell is positive what is the sign of gibbs free energy
negative, the rxn is spontaneous
Delta G=
in relation to emf
-nFE
Faradays constant
96485 C/mol
nernst equation
E= Estandard - (RT/nF) *ln(Q)
concentration cell
a volatic cell that is made with the same chemical species with diff concentrations in each half cell
portable, self containted electrical power souce with one or more volatic cell
battery
non rechargeable battery
primary cell
rechargeable battery
secondary cell
lead acid battery
used in cars, toxic reactants, rechargeable
alkaline battery
non rechargeable, lightweight, most popular primary battery
AA and AAA batteries
Ni-Cd/metal battery
secondary cell, found in electronics, cadmium not around anymore bc/ toxic
Are fuel cells batteries?
No, they need a constant supply of fuel to operate
voltaic cell that uses H2 or CH4 to turn chemical E into electrical E
Fuel cell
Corrosion
Spontaneous redox reaction that involved the degredation of a metal by another substance
ex: rusting
Examples of corrosion prevention
- painting over metal (not the best option)
- cathodic protection (ex: galvanized iron)
when zinc is placed over iron to protect it from rusting because zinc has a lower reduction value so it will oxidize more easily
galvanized iron
non spon redox reactions driven by electrical E
electrolysis
Q=
Q here equals coulombs
It=nF
n= number of moles of e- through the wire
protons + neutrons =
mass number
number of protons
atomic number
Does the mass number go on the top or on the bottom?
top, atomic number goes on the bottom
Alpha decay
stream of alpha particles (4/2He)
Beta decay
emission of high energy electrons, increases number of protons
gamma decay
emission of high energy photons, does not change neutrons or protons
Positron emission
emits positron/ anti electron, opposite of beta decay bc it increases neutrons
electron caputre
nucleus captures electron from electron cloud, increases neutrons
all nuclei with more than — protons are radioactive
84
if a nucleus is above the band of stability what kind of decay does it undergo?
high neutron to proton ratio
beta decay to increase protons and decrease neutrons
if a nucleus is below the band of stability what kind of decay does it undergo?
low neutron to proton ratio
positron emission or electron caputre to increase the number of neutrons
True or false? A nucleus with an even number of protons is more likely to be stable than one with an odd number?
True
changes in the nucleus because of contact with another particule
Nuclear transmutations
Radioactive deacy is a — order process
1st order
first order half life
k = .693/ t1/2
or t1/2 = .693/k
True or false half lives for nuclear decay are affected by external factors like Temp, pressure, state of matter, etc.
False half life is unaffected by these factors
ln(Nt/N0) =
-kt
the rate at which a sample decays
disentegrations per unit of time
activity
1 bequerel =
1 disentigration per second
1 curie =
3.7*10^10 disentigrations per second
phosphors
substances that emit light when radioactive particles strike them
count the number of light flashes emitted by phosphors
scintillian counter
radiotracers
follows the path of an elements through a reaction, used to better understand reacton mechanisms
change in E/E=
change in m * c^2/ m*c^2
speed of light =
2.9979*10^8
Nuclear binding Energies
the amount of energy necessary to seperate a nucleus into its nucleons
fission
separating a heavy nucleaus into a smaller more stable one
fusion
combining smaller nuclei into larger more stable ones
if the mass of the nucleus is too large (supercritical mass) the reaction escalates into a violent explosion
chain reaction
critical mass
the amount of fissionable material needed to maintain a constant rate of fission
super critical mass
mass is too large and creates a chain reaction
too much fissionable material
subcritical mass
mass is not enough and no reaction occurs but materials are still radioactive
not enough fissionable material
fissionable material in a nuclear reactor
enriched uranium
fuel elements
absorb neutrons to keep a consant rate of fission and no over heating
control rods
slows down neutrons so they are more easily captured and then produce fission
moderator
ex: water or graphite
carry heat away from reaction
primary coolant
carries heat from primary coolant to turn turbine
secondary coolant
why is fusion not used to generate nuclear power right now?
The conditions it requires is too extreme to happen on earth right now
really high temperature and pressures
what kind of radiation is more harmful? Ionized or non ionized?
Ionized radiation is more harmful because it strips water molecules and creates harmful free radicals (OH)
alpha, beta, gamma
the gray
measure of radiation
1 J of E per kg/tissue
rad (radiation absorbed dose)
measure of radiation
1*10^-2 J of E per Kg/tissue
1 Gy =
100 rad
RBE (relative biological effectiveness) =
1 in gamm and beta = 10 for alpha
effective dossage =
can be sieverts
number of rad * RBE
1 Sv=
100 rem
