Test 2 – Chemistry Flashcard

Thermodynamics
the science of heat and work
Energy
capacity to do work or transfer heat
Kinetic energy
energy of motion:
thermal-motion of particulate level
mechanical-motion of macroscopic objects
electrical-motion of electrons through conductor (redox, batteries)
potential energy
results from position:
gravitational-energy possessed at certain height
chemical-energy in fuels
electrostatic-energy associated w/separation of two electrical charges (atoms attract to form bonds, lowers potential)
temperature
measure of its ability to transfer energy as heat (determines direction of thermal energy transfer.. higher temp = higher thermal energy)
system/surroundings
system is object being studied, surroundings are everything outside the system that can exchange energy/matter w/the system
exothermic process
energy transferred as heat from a system to its surroundings (energy of system decreases, energy of surroundings increases)
endothermic process
energy is transferred as heat from the surroundings to the system (energy of system increases, energy of surroundings decreases)
calorie
energy transferred as heat that is required to raise the temp of 1 g pure water 10 degrees (1 cal = 4.184 J)
energy depends on:
quantity of material, magnitude of temp change, identity of material gaining or losing energy
specific heat capacity
energy transferred as heat that’s required to raise the temp of 1 g of a substance by 1 K q=cmT (intensive property)
heat of fusion
energy transferred as heat that’s required to convert a substance from a solid at its melting point to a liquid
heat of vaporization
energy transferred as heat to convert a liquid at its boiling point to a vapor. Added energy is used to overcome forces holding the molecules together, not to increase the temp, which stays the same as the state changes)
energy and work
if a system does work on its surroundings it expends energy (system’s energy decreases as surroundings’ energy increases). if work is done by the surroundings, the system gains energy
first law of thermodynamics
U=q + W all energy transfers b/w a system and the surroundings occur by processes of heat and work
internal energy, U
KE + PE
energy transferred as heat:
to the system(endothermic) -q(+)-U increases
from the system(exothermic)-q(-)-U decreases
work done on system-W(+)- U increases
work done by system-W(-)-U decreases
enthalpy, H
H=U+PV heat energy transferred at constant pressure
-H : energy as heat from system to surroundings
+H : energy as heat from surroundings to system
standard reaction enthalpy
enthalpy change of a reaction that occurs w/all reactants and products in their standard states
– for exothermic, + for endothermic
calorimetry
measures energy evolved/required as heat in a chemical/physical process. Change happens as chemical reaction occurs; energy is gained/lost as heat by the solution
Hess’s law
if a reaction is the sum of 2+ other reactions, standard reaction enthalpy for the overall process is the sum of the standard reaction enthalpies of those reactions
standard molar enthalpies of formation
enthalpy change for the formation of 1 mol of a compound directly from its component elements in their standard states.
is zero for element in standard state.
most values are – (exothermic)
product favored
reactions where reactants are largely converted to products at equilibrium (- values of standard reaction enthalpy)
reactant favored
reactions where only a small amount of products are present at equilibrium (+ values of standard reaction enthalpy)
electromagnetic radiation
radiation that consists of wave-like electric and magnetic fields
Plank’s energy eqn
E=nhv where h is plank’s constant (6.63e-34 J s), v is frequency. energy is quantized (only certain energies allowed)
photoelectric effect
electrons are ejected when light strikes the surface of a metal if the frequency of light is high enough (shows that light can behave as particles)
photons
energy of each photon is proportional to the frequency of radiation (photons striking atoms on a metal surface will eject electrons iff. photons have enough energy)
potential energy of electron in nth energy level
E=-Rhc/n^2 R is Rydberg constant (R=1.0974e7), h is plank’s constant
to move an electron from ground state to higher state energy must be absorbed. if electron falls from higher n to lower n energy is released
lyman series
electron falls from n>1 to n=1
balmer series
electron falls from n>2 to n=2
Heisenberg’s uncertainty principle
any attempt to accurately determine either the location or energy of an electron will leave the other uncertain
quantum mechanics
uses mathematical eqns of wave motion to generate a series of eqns called wave eqns:
1. an electron in the atom is described as a standing wave 2. by defining the electron as s standing wave, quantization is introduced into the description of electronic structure 3. each wave fxn is associated w/an allowed energy value 4. the value of the wave fxn at a given point in space is the amplitude of the wave 5. at any point in space, the square of the value of the wave fxn defines the probability of finding the electron (electron density) 6. Schrodinger’s theory defines energy of electron, uncertainty principle says there is uncertainty in is location, so we describe the probability of the electron being w/in a certain region in space when in a given energy state
principle quantum number, n
primary factor in determining the energy and size of an orbital (greater n = greater size of orbital). same n value: electrons in same electron shell
azimuthal quantum number, l
defines characteristic shape of an orbital:
l=0, s subshell
l=1, p subshell
l=2, d subshell
l=3, f subshell
magnetic quantum number, m(l)
related to orientation in space of orbitals w/in a subshell (ranges from -l to l where 2L +1 is the # orbitals in subshell m(l)
s orbitals
n=1, l=0, most likely found near nucleus, spherical, has boundary surface, max electrons: 2
p orbitals
l=1, dumbbell shape, three p orbitals in a subshell, max electrons: 6
d orbitals
l=2, 5 d orbitals, “donut”, max electrons: 10
f orbitals
l=3, electron density in 8 regions of space, max electrons: 14
electron spin quantum number, m(s)
if atoms w/a single unpaired electron are placed in a magnetic field, there are 2 orientations for the atoms: spin aligned with or opposed to the field
m(s) is quantized: =+/- 1/2
paramagnetism
attraction to a magnetic field of substances in which the constituent ions or atoms contain unpaired electrons
pauli’s exclusion principle
no two electrons in an atom can have the same set of four quantum numbers(n,l,m(l), m(s))
aufbau principle
procedure that assigns electrons to orbitals. assigned to n shells and l subshells inorder of increasingly higher energy
rules to predict arrangements of electrons
1. electrons are assigned to subshells in order of increasing “n & l” values
2. for two subshells w/the same value of n & l, electrons are first assigned to the subshell of lower n
effective nuclear charge, Z*
net charge experienced by a particular electron in a multielectron atom resulting from the nucleus and other electrons
going across a period, Z* increases (increases attraction b/w nucleus and valence electrons)
s>p>d>f
hund’s rule
the most stable arrangement of electrons is that w/the max # of unpaired electrons, all w/the same spin direction
atomic radii
for main group elements: radii increase going down a group and decrease going across a period (due to Z*)
ionization energy, IE
energy required to remove an electron from an atom in gas phase. to separate an electron from an atom energy must be supplied to overcome attractive nuclear charge. each subsequent electron requires more energy for removal
electron affinity, EA
energy change for a process in which an electron is acquired by the atom in the gas phase. the greater the EA the lower the energy of the ion (high IE means more -EA)
isoelectronic ions
same # electrons but different # protons. as # protons increases in a series of isoelectronic ions, the balance b/w electron-proton attraction and electron-electron repulsion shifts in favor of attraction and the radius decreases

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