Chem 330 final Flashcards
what is the differential rate law (often called just the rate law)
expresses how the rate depends on concentration
rate/concentration
what is the integrated rate law
expresses how the concentration depends on time
concentration/time
if a reaction is first order with respect to a reactant, how does the concentration of the reactant affect the reaction rate
doubling the concentration of the reactant doubles the reaction rate
what is the method of initial rates
several experiments are carried out using different initial concentrations and the initial rate is determined for each run. the results are then compared to see how the initial rate depends on the initial concentrations
what is the half life of a reaction
the time required for a reactant to reach half of its original concentration
for a first order reaction, does half life depend on initial concentration
no, it depends only on k
for a second order reaction, does half life depend on initial concentration
yes, it depends both on initial concentration and on k
for a second order rxn, how is each half life related to the next one
each successive half life is double the preceding one
what is a pseudo first order rate law
a rate law obtained by simplifying a more complicated one; i.e. when the concentration of 2 reactants is so large compared to a third that the 3 large can be considered constant
what is an elementary step
a reaction whose rate law can be written from its molecularity
what is molecularity
the number of species that must collide to produce the reaction indicated by that step
what is a unimolecular step
a rxn involving one molecule
what is a bimolecular rxn
rxns involivng the the collision of two species
what is a termolecular rxn
rxns involivng the the collision of 3 species
what is a reaction mechanism
a series of elementary steps that must satisfy two requirements:
(1) the sum of the elementary steps must give the overall balanced equation
(2) the mechanism must agree with the experimentally determined rate law
what is the rate-determining step in a reaction
the slowest step b/c a reaction is only as fast as its slowest step so this step determines the rate
how does temperature affect the speed of a reaction
chemical reactions speed up when temperature is increased
what is activation energy
a threshold energy that must be overcome to produce a chemical reaction
why do only a small fraction of collisions produce a reaction
b/c the collisions need to have enough energy to overcome the activation energy and because the collisions need to have the correct orientations
how is activation energy related to the speed of a reaction at a given temperature
the higher the activation energy, the slower the reaction
what is the activated complex/transition state
the arrangement of atoms found at the top of the potential energy ‘hill’ or barrier
how do catalysts make reactions go faster
they provide a new pathway for the reaction to occur, and this pathway has a lower activation energy; this allows a much larger fraction of the collisions to be effective at a given temperature
do catalysts affect the energy difference between products and reactants?
no
what is wavelength
the disance between two consecutive peaks or troughs in a wave
what is frequency
the number of waves per second that pass a given point in space
how are wavelength and prequency related
inversely proportional
in what quantities is energy gained/lost
only in whole number multiples; energy is quantized and can be transferred only in discrete units of size hv
what are the small ‘packets’ of energy called
quantum; a system can transfer energy only in whole quanta
what are photons
particles representing a quantum of light or other electromagnetic radiation
what is the photoelectric effect
refers to the phenomenon in which electrons are emitted from the surface of a metal when light strikes it
what 4 observations characterize the photoelectric effect
- no electrons are emitted by a given metal below a specific threshold frequency
- for a light w/ frequency lower than the threshold frequency, no electrons are emitted regardless of the intensity of the light
- for light w frequency greater than the threshold frequency, the number of electrons emitted increases with the intensity of the light
- for a light with frequency greater than the threshold frequency, the kinetic energy of the emitted electrons increases linearly with the frequency of the light
what does the threshold frequency represent for electromagnetic radiation
the minimum energy required to remove the electron from the metal’s surface
for light with frequency greater than the threshold frequency, where does the excess energy go
it is given to the electron as kinetic energy
when a system loses energy, what happens to its mass
it also loses mass
what is the dual nature of light
electromagnetic radiation exhibits wave properties and certain characteristics of particulate matter
what is the significance of the line spectrum of hydrogen
only certain energies are allowed for the electron in the hydrogen atom; the energy of the electron in the hydrogen atom is quantized
what is the heisenberg uncertainty principle
there is a fundamental limitation to just how precisely we can know both the position and the momentum of a particle at a given time; the more precisely we know position, the less precisely we know momentum, and vice versa
what is the pauli exclusion principle
in a given atom no two electrons can have the same set of 4 quantum numbers; each orbital can only hold two electrons and they must have opposite spins
what is hund’s rule
the lowest-energy configuration for an atom is the one having the maximum number of unpaired electrons allowed by the Pauli principle in a particular set of degenerate orbitals
