Chemistry - Ch 14

Question 1

Chemical kinetics

Answer 1

the area of chemistry that is concerned with the speeds, or rates, of reactions

Question 2

Reaction rate

Answer 2

the speed of a chemical reaction; change in the concentration of reactants or products per unit of time; units usually molarity per second (M/s)

Question 3

Instantaneous rate

Answer 3

the rate at a particular moment in the reaction

Question 4

Beer’s Law

Answer 4

relates the amount of light being absorbed to the concentration of the substance absorbing the light

Question 5

Rate law

Answer 5

an equation which shows how the rate depends on the concentration of reactants; generally has the form Rate = k[A]^m[B]^n

Question 6

Rate constant

Answer 6

the constant k in the rate law; magnitude of k changes with temperature and therefore determines how temperature affects rate

Question 7

Reaction orders

Answer 7

exponents m & n in a rate law

Question 8

Overall reaction order

Answer 8

sum of the orders with respect to each reactant in the rate law

Question 9

First order reaction

Answer 9

one whose rate depends on the concentration of a single reactant raised to the 1st power

Question 10

Differential rate law

Answer 10

the form of a rate law, which expresses how rate depends on concentration

Question 11

Integrated rate law

Answer 11

ln[A] subscript t - ln[A] subscript 0 = -kt OR ln ([A] subscript t/[A] subscript 0) = -kt

Question 12

Second order reaction

Answer 12

one whose rate depends on the reactant concentration raised to the 2nd power or on the concentrations of 2 different reactants, each raised to the 1st power; rate = k[A]^2

Question 13

Half-life

Answer 13

time required for the concentration of a reactant to reach one-half of its initial value

Question 14

Collision model

Answer 14

based on the kinetic-molecular theory, accounts for concentration of reactants and temperature at the molecular level; central idea: molecules must collide to react

Question 15

Activation energy

Answer 15

the minimum energy required to initiate a chemical reaction (E subscript a)

Question 16

Activated complex (transition state)

Answer 16

particular arrangement of atoms at the top of the barrier (barrier = energy necessary to force the molecule through the relatively unstable intermediate state to the final product)

Question 17

Arrhenius equation

Answer 17

most reaction-rate data obeyed an equation based on 3 factors: (1) fraction of molecules possessing an energy of E subscript a or greater (2) the # of collisions per second, & (3) the fraction of collisions that have the appropriate orientation; k=Ae^(-E subscript a/RT)

Question 18

Frequency factor

Answer 18

A from Arrhenius equation; related to the frequency of collisions and the probability that the collisions are favorably oriented for reaction

Question 19

Reaction mechanism

Answer 19

process by which a reaction occurs

Question 20

Elementary reactions (elementary processes)

Answer 20

single collision (event, step)

Question 21

Molecularity

Answer 21

number of molecules that participate as reactants in an elementary reaction

Question 22

unimolecular

Answer 22

a single molecule is involved in a reaction

Question 23

bimolecular

Answer 23

elementary reactions involving the collision of 2 reactant molecules

Question 24

termolecular

Answer 24

elementary reactions involving the simultaneous collision of 3 molecules

Question 25

intermediate

Answer 25

a substance that is neither a reactant nor a product in the overall reaction (formed in 1 elementary reaction and consumed in the next); multistep mechanisms involve 1 or more of these

Question 26

Rate-determining step

Answer 26

overall rate of a reaction cannot exceed the rate of the slowest elementary step of its mechanism; b/c the slow step limits the overall reaction rate, it is the _____ ______ _____.

Question 27

Catalyst

Answer 27

substance that changes the speed of a chemical reaction without undergoing a permanent chemical change itself in the process

Question 28

Homogeneous catalyst

Answer 28

a catalyst that is present in the same phase as the reacting molecules

Question 29

Heterogeneous catalyst

Answer 29

exists in a different phase from the reactant molecules, usually as a solid in contact with either gaseous reactants or with reactants in a liquid solution

Question 30

adsorption

Answer 30

initial step of heterogeneous catalysis; refers to the binding of molecules to a surface

Question 31

absorption

Answer 31

uptake of molecules into the interior of another substance

Question 32

enzymes

Answer 32

efficient biological catalysts; necessary for many reactions in the body to occur at suitable rates

Question 33

Active site

Answer 33

reaction is catalyzed at a very specific location in an enzyme

Question 34

substrates

Answer 34

substances that undergo reaction at this site

Question 35

lock-and-key model

Answer 35

simple explanation for the specificity of an enzyme

Question 36

nitrogen fixation

Answer 36

process of converting N2 into compounds that plants can use

Question 37

enzyme inhibitors

Answer 37

substances that bind strongly to the active site and block the entry of the substrate