Exam 3

Question 1

(T/F) All molecules in a gas have the same speed.

Answer 1

False, they do NOT have the same speed.

Question 2

What is the relationship between gamma and temperature?

Answer 2

inverse relationship

Question 3

When does effusion occur?

Answer 3

when the diameter of the hole is smaller than the mean free path (lambda)

Question 4

What is diffusion?

Answer 4

transport of matter due to concentration gradient

Question 5

What is Fick’s first law? Write it out.

Answer 5

flux goes from regions of high concentration to regions of low concentration, with a magnitude that is proportional to the concentration gradient; write out Dineli’s notes, bottom of page 4

Question 6

What is flux?

Answer 6

amount of matter passing through unit area in unit time

Question 7

What is thermal transport?

Answer 7

transport of energy down a temperature gradient

Question 8

What is the energy of each molecule of a monatomic gas?

Answer 8

3/2kBT

Question 9

What did Arrhenius say in 1889? (2)

Answer 9

Van’t Hoff equation for temperature dependence of the equilibrium constant is (dlnKc/dT) = (deltaH/RT^2); law of mass action relates the equilibrium constant to the ratio of the forward and backward rate constants kc = k1/k-1

Question 10

What is the physical interpretation of the e^(-Ea/RT) term in the Arrhenius equation?

Answer 10

fraction of reactant with enough energy to react

Question 11

What is the idea behind the Lindemann mechanism?

Answer 11

unimolecular reactions proceed because the reactant molecule is energized by a partner molecule in collision; concentration of energized reactant molecule is very small so invoke steady-state approximation

Question 12

What are the k1/k-1/k2/k-2/k3/k-3 term names in chain reactions?

Answer 12

k1 = initiation, k-1 = termination, k2 = propagation, k-2 = inhibition, k3 = propagation, k-3 = inhibition

Question 13

Define physisorption.

Answer 13

attractive forces between substrate and adsorbate arise from van der Waals interactions.

Question 14

Define chemisorption.

Answer 14

adsorbate bound to surface by covalent or ionic forces

Question 15

Define adsorption isotherm.

Answer 15

plot of surface coverage as a function of gas pressure at constant temperature

Question 16

What happens in a temperature jump experiment?

Answer 16

temperature of the equilibrium reaction mixture is
suddenly changed at constant pressure; following change in temperature, chemical system responds by relaxing to a new equilibrium state that corresponds
to new temperature

Question 17

What does the value tau in the temperature jump experiment represent?

Answer 17

amount of time it takes to decay to 1/e of initial value

Question 18

How do we calculate tau, given k1, k-1, and the equilibrium concentrations of A and B at the new temperature?

Answer 18

write out Dineli’s Exam 4 Notes, Page 50

Question 19

Write out the Arrhenius expression for a rate constant.

Answer 19

write out Dineli’s Exam 4 Notes, Page 51

Question 20

What is the Transition State Theory? (2)

Answer 20

rate of reaction is the number of activated complexes passing per second over the top of the potential energy barrier; reactant is the activated complex (AB#) in equilibrium with each other (invoking steady state)

Question 21

What are the three main differences between the Arrhenius theory and Transition State theory?

Answer 21

TST uses concept of free energy, but Arrhenius does not; arbitrary factor of A in Arrhenius expression (result of integration) but specific factor in TST; similar activation energy term in both expressions

Question 22

Write out the chemical equations for the Lindemann mechanism.

Answer 22

write out Dineli’s Exam 4 Notes, Page 52

Question 23

What is the general idea behind the steady state approximation?

Answer 23

the concentration of the energized molecule in the Lindemann mechanism is very small, and changes to it can be ignored

Question 24

In the Langmuir adsorption model, what does theta represent?

Answer 24

the fraction of surface sites occupied by an absorbate

Question 25

Write out the equation for theta in the Langmuir adsorption model. Identify each component.

Answer 25

write out Dineli’s Exam 4 Notes, Page 54

Question 26

What is the primary difference between the Langmuir and BET models?

Answer 26

Langmuir — monolayer formation; BET — multilayer formation; BET tends to take longer to completely cover the surface since multilayers start to form before the monolayer is covered