Unit 4 (ch 19) Flashcards
batteries produce energy via
spontaneous redox processes
redox chemistry
e- gained or lost through reduction and oxidation
oxidation
losing e-
reduction
gaining e-
something that is oxidized is a
reducing agent
electrochemical cells
two physically separated half cells
use e red values to determine
cell potential
cell potential
measure of force pushing e+ from anode to cathode
E cell=
E cathode (reduced) - E anode (oxidized)
movement of electrons from anode to cathode produces
electrical work
E cell should always be
positive
delta G cell
welec
welec=
nFEcell, moles x faraday x ecell= J
C=
n x F
faradays constant
9.65x10^4
welec measures
energy associated with electrochemical cell
standard hydrogen electrode cathode
II H+(1 M) I H2(g), 1atm I Pt
standard hydrogen electrode anode
Pt I H2(g), 1atm I H+ (aq, 1 M) II
How can delta G relate to batteries?
delta G = -n x F x Ecell
non standard E cell =
E cell (standard) - RTlnQ/ (nF)
as Q increases,
0.0592 / n log Q also does
increase concentration =
increase E red
< 1 M =
decreasing E cell
> 1 M =
increasing E cell
finding k
log k = n x E cell/ (0.0592)
k < 1
E cell < 0 (reactants)
k > 1
E cell > 0 (products)
how to determine battery capacity
w elec = - C x E cell
1 ampere =
1 coulomb/second
1 coulomb =
1 amp x sec
1 C V =
1 J
1 J=
1 A x s x V
1 watt =
volts x current (J/s)
1 w =
1 J/s
1 kw=
1000 J/s
1 kw x hr=
1000 w x hr
1 watt =
1 A x V
Why are batteries important and why would it be good if they were improved?
- power many aspects of our lives
- lighter, higher capacity batteries would increase the efficiency and utility of battery powered devices
voltaic cell
energy generated by spontaneous redox processes
electrolytic cell
recharging reverses the process
oxidation occurs at the
anode
reduction occurs at the
cathode
electrochemical reactions consist of
two half reactions which must be electrochemically balanced
standard potential of cell is calculated how?
- use standard reduction potentials
- Ecell= Ecathode-Eanode
more positive reduction potential is
cathode
movement of electrons from anode to cathode (blank)
produces electrical work
what are the standard conditions for E not cell?
1 atm and 1 M
E not cell values are not dependent on (blank)
stoichiometry
delta G cell
- nFEcell
Delta G cell relates
work and free energy of the system
moles of electrons (n) is
number gained or lost
How many moles (n) does this equation have?
Cu^2+ +Zn(s)–> Zn2+ + Cu(s)
most of our e not cell values are relative to the
standard hydrogen electrode
if you are at 298 K, Ecell =
E not cell - (0.0592 log Q/ n)
At equilibrium, logK
n E not cell / 0.0592
1 C V =
1 J
1 J =
1 AsV
1 W=
1 J/s
1 As =
1C
what are the conversions of batteries used for
determine how long it takes to recharge a battery
What are uses of nuclear chemistry?
- energy (fusion and fission)
- climate science
- medical scanning (CT and PET)
- archaeology
- smoke detectors
- x- rays
- food preservation
- cancer treatments
Nuclear chemistry helps us understand
how universe began
describe neutron stability
not stable and decay into proton and electron
matter can be transformed to energy (equation)
E= mc^2
radioactive decay is
first order
what does it mean by first order?
depends only on how many radioactive ions/isotopes we have
radioactive decay is measured by
half life
half life equation
n= t/ t 1/2
Nt/N0=
0.5^ n or 0.5^t/t1/2
fusion of nuclei gives
larger nuclei, often giving off positrons or other particles in the process
positrons
are anti-matter and combine with electrons to annihiliate and produce a gamma ray
binding energy
determine mass difference between starting (proton/neutrons) and final nucleus mass, determine E
nucleus held together by
strong force
when can larger nuclei go through different decay processes
if they aren’t stable
isotope with higher mass number
neutron rich and decay by beta decay
beta decay
give off electron as neutron converts to proton
unstable isotope lighter than stable
neutron poor, positron emission or electron capture, more neutrons
larger isotopes often go through
alpha decay
alpha decay
alpha particle (helium nucleus) lost
After what element are all species radioactive? Why?
Bismuth
-repulsive forces between protons too strong
how to make bigger nuclei?
decay processes, smash nuclei with neutrons or other nuclei
how can we make gold?
smash nuclei with neutrons or other nuclei to build bigger ones
current nuclear energy applications rely (blank)
nuclear fission
describe nuclear fission
235U captures neutron, becomes 236 U, which quickly decomposes to generate other smaller nuclei and neutrons, which keep process going
radioactivity is measure in
curies (Ci) or becquerels (Bq)
rate of decay =
A= kN
radiometric dating takes advantage of (blank)
radioactive isotopes with known half-lives to determine age based on amount of remaining radioactivity
what is used to date rocks?
235 U
what is used to date formerly living things?
14 C
Why is radiation bad for living things?
has lots of energy and can form highly reactive species like hydroxyl radicals with can react with proteins and DNA
Ionizing radiation/mass is measured in
Grays (Gy)
1 Gy=
1 J/kg
how determine damage related to ionizing radiation
Gy(RBE) = Sievert
RBE
relative biological effectiveness
Sievert
SI unit for effective dose
as energy is transformed into matter, what is formed?
unstable things, e= mc^2
fusion of hydrogen nuclei to form helium
1/1 p + 1/0 n –> 2/1 d
2 2/1 d—> 4/2 alpha
1/1 p + 1/1 p –> 2/1 d + 0/1 B
posititrons and electrons (blank) to release huge amounts of energy
annihilate each other
overall equation of positrons and electrons annihilation
4 1/1 p –> 4/2 He + 2 0/1 B
4 protons lose mass for form
alpha particle
mass of stable nucleus (blank) than free nucleons
less
BE
delta m c^2
radioactive ones on belt of stability
radionuclides
above belt of stability
neutron rich, beta decay
below belt of stability
neutron poor, positron emission
beta decay
gain proton
14/6 C –> 14/7 N + 0/-1 B
positron emission
10/6 C –> 10/5B +0/1 B
lose proton
electron capture
11/6 C + 0/-1 B –> 11/5 B
lose proton
written opposite positron
alpha decay
234/92 U –> 4/2 alpha + 230/90 Th
subtract 4 and 2
after 83 protons, all species are
radioactive
nuclei with (blank) tend to be more stable
even # protons and neutrons
nuclear fission involves
decomposition of U nucleus
produce > 1 neutron, process is
self-sustaining
radioactivity measured as
decay event/time
radioactivity is a
first order process
radioactivity rate =
decay events atom/sec times number of atoms
good for dating rocks
235 U and 207 Pb
biological effects of radiation
- forms of radiation can break chemical bonds
- produce radicals, free electrons, cations
- “ionizing radiation”
- cause cancer, birth defects, death
absorbed dose measures
ionizing radiation/mass
SI unit—>
G ray = 1 J/kg
Gy RBE=
Sievert
what occurs since alpha particles have a large mass?
blocked with paper
one way to have exposure to alpha particles is
radon gas
