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Chemistry 3321 > Exam 3 > Flashcards

Exam 3 Flashcards

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1
Q

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

A

False, they do NOT have the same speed.

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2
Q

What is the relationship between gamma and temperature?

A

inverse relationship

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3
Q

When does effusion occur?

A

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

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4
Q

What is diffusion?

A

transport of matter due to concentration gradient

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5
Q

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

A

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

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6
Q

What is flux?

A

amount of matter passing through unit area in unit time

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7
Q

What is thermal transport?

A

transport of energy down a temperature gradient

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8
Q

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

A

3/2kBT

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9
Q

What did Arrhenius say in 1889? (2)

A

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

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10
Q

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

A

fraction of reactant with enough energy to react

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11
Q

What is the idea behind the Lindemann mechanism?

A

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

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12
Q

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

A

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

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13
Q

Define physisorption.

A

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

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14
Q

Define chemisorption.

A

adsorbate bound to surface by covalent or ionic forces

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15
Q

Define adsorption isotherm.

A

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

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16
Q

What happens in a temperature jump experiment?

A

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

17
Q

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

A

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

18
Q

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

A

write out Dineli’s Exam 4 Notes, Page 50

19
Q

Write out the Arrhenius expression for a rate constant.

A

write out Dineli’s Exam 4 Notes, Page 51

20
Q

What is the Transition State Theory? (2)

A

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)

21
Q

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

A

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

22
Q

Write out the chemical equations for the Lindemann mechanism.

A

write out Dineli’s Exam 4 Notes, Page 52

23
Q

What is the general idea behind the steady state approximation?

A

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

24
Q

In the Langmuir adsorption model, what does theta represent?

A

the fraction of surface sites occupied by an absorbate

25
Q

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

A

write out Dineli’s Exam 4 Notes, Page 54

26
Q

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

A

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

Chemistry 3321 (3 decks)

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