Chemical Kinetics

Question 1

what is an intermediate

Answer 1

molecules that exist within the course of a reaction but are neither reactants or products

Question 2

what is the rate-determining step

Answer 2

the slowest step in any proposed mechanism

Question 3

what is collision theory of chemical kinetics

Answer 3

states that the rate of a reaction is proportional to the number of collisions per second between the reacting molecules
suggests that not all collisions are strong enough/in the right orientation to result in a chemical reaction

Question 4

what is the activation energy

Answer 4

the minimum energy for a reaction to proceed and form new bonds

Question 5

what is the arrhenius equation

Answer 5

A = frequency factor
as A increases, the rate constant also increases
T = temperature
as T increases, the rate constant also increases

Question 6

rate of reaction equation

Answer 6

Z x f
where Z is the total number of collisions occurring per second and f is the fraction of collisions that are effective

Question 7

what is the frequency factor

Answer 7

aka the attempt frequency of the reaction
a measure of how often molecules in a certain reaction collide (with the unit s^-1)
can be increased by increasing the number of molecules in a vessel because it creates more opportunities for collision

Question 8

what is the transition theory

Answer 8

states that when molecules collide with energy equal to or greater than the activation energy, they form a transition state in which the old bonds are weakened and the new bonds begin to form
the transition state then dissociates into products
the transition state has greater energy than both the products and reactants

Question 9

what is the free energy of the reaction

Answer 9

the difference between the free energy of the products and the free energy of the reactants

Question 10

a negative free energy change indicates

Answer 10

an exergonic reaction (energy is given off)

Question 11

a positive free energy change indicates

Answer 11

an endergonic reaction (energy is absorbed)

Question 12

factors affecting reaction rate

Answer 12

reaction concentrations, temperature, medium, and catalysts

Question 13

how does reaction concentration affect reaction rate

Answer 13

the greater the concentration of the reactants, the greater the number of effective collisions per unit time
this is will increase reaction rate for all but zero-order reactions

Question 14

how does temperature affect reaction rate

Answer 14

the reaction rate will increase as temperature increases

Question 15

how does medium temperature affect reaction rate

Answer 15

some molecules are more likely to react with each other in aqueous environments, while others are more likely to react in nonaqueous environments (DMSO or ethanol)
the physical state of the medium also plays a role (solid, liquid gas)
generally polar solvents are preferred

Question 16

how do catalysts affect reaction rate

Answer 16

they increase the reaction rate by lowering the activation energy for both forward and reverse reactions
they are not consumed in the reaction

Question 17

the rate law equation

Answer 17

= k[A]^x[B]^y
where k is the reaction rate coefficient or rate constant, x and y are the orders of the reaction

Question 18

what is a zero-order reaction

Answer 18

a reaction where the rate of formation of product C is independent of changes in concentrations of any of the reactants (A and B)
these reactions have a constant reaction rate equal to the rate constant (k)
although the reaction rate if independent of changes in concentration of A and B, it can be changed by temperature or the addition of a catalyst

Question 19

the rate law for a zero-order reaction

Answer 19

rate = k [A] ^ 0 [B] ^ 0 = k
k has the units M/s

Question 20

zero-order reaction graphed

Answer 20

on a concentration/time curve, is linear
the slope is the opposite of the rate constant (-k)

Question 21

what is a first-order reaction

Answer 21

a reaction that has a rate that is directly proportional to only one reactant

Question 22

the rate law for a first-order reaction

Answer 22

rate = k [A] or rate = k [B]
k has the units s^-1

Question 23

first-order reaction graphed

Answer 23

on a concentration/time curve results in a nonlinear graph - shows that the product is dependent on the concentration of the reactant
on a ln[A]/time graph curve is linear (-k)

Question 24

what is a second-order reaction

Answer 24

a reaction that has a rate that is proportional to either the concentration of two reactants or to the square of the concentration of a single reactant
often suggests a physical collision between two reactant molecules

Question 25

rate law for second-order reaction

Answer 25

rate = k [A] ^1 [B] ^1
or
rate = k [A] ^2
or
rate = k [B] ^ 2

Question 26

second-order reaction graph

Answer 26

on a concentration/time graph curve is nonlinear
on a 1/[A]/time graph, reveals a linear curve where the slope of the curve is k (positive)

Question 27

what is a higher-order reaction

Answer 27

where three particles collide simultaneously with the correct orientation and sufficient energy to undergo a reaction

Question 28

what are mixed-order reactions

Answer 28

reactions that sometimes refer to non-integer orders (fractions) or have varying rate orders over the course of the reaction

Question 29

rate law for mixed-order

Answer 29

rate = (k1 [C][A]^2) / k2 + k3 [A]
A= single reactant
C= catalyst
when A is large, k3[A] > k2 and appears first-order
when A is low, k2 > k3[A] and appears second-order