CHM 142 exam 4 Flashcards by Melina Balch

the study of electricity and chemical reactions

electrochemistry

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half- reactions

equations that only show oxidation or reduction alone

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electrons are shown as— in oxidation

products

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electrons are shown as — in reduction

reactants

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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)

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voltaic cell

a device that facilitates the transfer of electrons externally by a wire instead of directly through the reactants

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loses mass over time, negative, where oxidation occurs, anions flow to this

anode

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gains mass over time, positive, where reduction occurs, cations flow to this

cathode

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what is the purpose of a salt bridge in a voltaic cell?

to keep the solutions neutral so electrons flow from anode to cathode

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electrons flow—from the anode to the cathode

spontaneously

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the potential difference between two electrodes of a voltaic cell

cell potential/emf/Ecell

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Ecell=

Ecathode-Eanode

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the more — a Ecell value is the more likely it is for — to occur

positive, reduction

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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

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Does changing the coefficents in a rxn equation change the cell potential?

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if the value of Ecell is negative the rxn is —

nonspontaneous

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If the value of Ecell is positive what is the sign of gibbs free energy

negative, the rxn is spontaneous

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Delta G=

in relation to emf

-nFE

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Faradays constant

96485 C/mol

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nernst equation

E= Estandard - (RT/nF) *ln(Q)

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concentration cell

a volatic cell that is made with the same chemical species with diff concentrations in each half cell

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portable, self containted electrical power souce with one or more volatic cell

battery

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non rechargeable battery

primary cell

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rechargeable battery

secondary cell

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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

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

CHM 142 exam 4 Flashcards

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