Chem 330 final

Question 1

what is the differential rate law (often called just the rate law)

Answer 1

expresses how the rate depends on concentration

rate/concentration

Question 2

what is the integrated rate law

Answer 2

expresses how the concentration depends on time

concentration/time

Question 3

if a reaction is first order with respect to a reactant, how does the concentration of the reactant affect the reaction rate

Answer 3

doubling the concentration of the reactant doubles the reaction rate

Question 4

what is the method of initial rates

Answer 4

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

Question 5

what is the half life of a reaction

Answer 5

the time required for a reactant to reach half of its original concentration

Question 6

for a first order reaction, does half life depend on initial concentration

Answer 6

no, it depends only on k

Question 7

for a second order reaction, does half life depend on initial concentration

Answer 7

yes, it depends both on initial concentration and on k

Question 8

for a second order rxn, how is each half life related to the next one

Answer 8

each successive half life is double the preceding one

Question 9

what is a pseudo first order rate law

Answer 9

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

Question 10

what is an elementary step

Answer 10

a reaction whose rate law can be written from its molecularity

Question 11

what is molecularity

Answer 11

the number of species that must collide to produce the reaction indicated by that step

Question 12

what is a unimolecular step

Answer 12

a rxn involving one molecule

Question 13

what is a bimolecular rxn

Answer 13

rxns involivng the the collision of two species

Question 14

what is a termolecular rxn

Answer 14

rxns involivng the the collision of 3 species

Question 15

what is a reaction mechanism

Answer 15

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

Question 16

what is the rate-determining step in a reaction

Answer 16

the slowest step b/c a reaction is only as fast as its slowest step so this step determines the rate

Question 17

how does temperature affect the speed of a reaction

Answer 17

chemical reactions speed up when temperature is increased

Question 18

what is activation energy

Answer 18

a threshold energy that must be overcome to produce a chemical reaction

Question 19

why do only a small fraction of collisions produce a reaction

Answer 19

b/c the collisions need to have enough energy to overcome the activation energy and because the collisions need to have the correct orientations

Question 20

how is activation energy related to the speed of a reaction at a given temperature

Answer 20

the higher the activation energy, the slower the reaction

Question 21

what is the activated complex/transition state

Answer 21

the arrangement of atoms found at the top of the potential energy ‘hill’ or barrier

Question 22

how do catalysts make reactions go faster

Answer 22

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

Question 23

do catalysts affect the energy difference between products and reactants?

Answer 23

no

Question 24

what is wavelength

Answer 24

the disance between two consecutive peaks or troughs in a wave

Question 25

what is frequency

Answer 25

the number of waves per second that pass a given point in space

Question 26

how are wavelength and prequency related

Answer 26

inversely proportional

Question 27

in what quantities is energy gained/lost

Answer 27

only in whole number multiples; energy is quantized and can be transferred only in discrete units of size hv

Question 28

what are the small 'packets' of energy called

Answer 28

quantum; a system can transfer energy only in whole quanta

Question 29

what are photons

Answer 29

particles representing a quantum of light or other electromagnetic radiation

Question 30

what is the photoelectric effect

Answer 30

refers to the phenomenon in which electrons are emitted from the surface of a metal when light strikes it

Question 31

what 4 observations characterize the photoelectric effect

Answer 31

1. no electrons are emitted by a given metal below a specific threshold frequency 2. for a light w/ frequency lower than the threshold frequency, no electrons are emitted regardless of the intensity of the light 3. for light w frequency greater than the threshold frequency, the number of electrons emitted increases with the intensity of the light 4. 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

Question 32

what does the threshold frequency represent for electromagnetic radiation

Answer 32

the minimum energy required to remove the electron from the metal's surface

Question 33

for light with frequency greater than the threshold frequency, where does the excess energy go

Answer 33

it is given to the electron as kinetic energy

Question 34

when a system loses energy, what happens to its mass

Answer 34

it also loses mass

Question 35

what is the dual nature of light

Answer 35

electromagnetic radiation exhibits wave properties and certain characteristics of particulate matter

Question 36

what is the significance of the line spectrum of hydrogen

Answer 36

only certain energies are allowed for the electron in the hydrogen atom; the energy of the electron in the hydrogen atom is quantized

Question 37

what is the heisenberg uncertainty principle

Answer 37

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

Question 38

what is the pauli exclusion principle

Answer 38

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

Question 39

what is hund's rule

Answer 39

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