Lecture 6

Question 1

Each elementary reaction has ___ significance. It describes ___________.

Answer 1

physical
it describes a single step between the conversion of reactants and products.
it also describes an actual physical event on the molecular scale

Question 2

Global reactions are just___________.

Answer 2

the result of a curve-fitting exercise over a limited range of conditions.

Question 3

True/False: There is not necessarily any physical meaning to reaction rate laws obtained for global reactions.

Answer 3

True

Question 4

What do reaction rates express?

Answer 4

A change in moles that occurs within a certain volume or within a certain weight of catalyst per unit of time.

Question 5

What is the units of reaction rate by volume (3 options)?

Answer 5

moles/(volumetime)
moles/(ft^3hr)
moles/(liter*sec)

Question 6

What is the units of reaction rate by weight of catalyst?

Answer 6

moles/(lbmin)
moles/(masstime)
moles/(kg*sec)

Question 7

True/False: Units are the same for elementary and global reactions?

Answer 7

True

Question 8

What are the two different ways to express reaction rate?

Answer 8

volume or weight of catalyst

Question 9

What is reaction order?

Answer 9

refers to the exponent to which the concentrations are raised

Question 10

What order is r=kfCa

Answer 10

First order

Question 11

What is the order of r=kfCa^2

Answer 11

second order

Question 12

What is the order of r=kfCaCb^2

Answer 12

third order

Question 13

What kind of coefficients and reaction orders do elementary reactions have?

Answer 13

integer: 1,2,3 etc

Question 14

What kind of coefficients and reaction orders do Global reactions have?

Answer 14

fractional, zero, or negative

Question 15

What does zero order mean?

Answer 15

There is no molecules that participate

Question 16

What does fourth order imply?

Answer 16

4 body collisions which are so rare as to be unimportant in our class

Question 17

True/False: Global reaction orders are contrained?

Answer 17

False they are not constrained.

Question 18

What do global reactions describe?

Answer 18

the net behavior of the reacting system, but not the individual steps required to get from the reactant to the products

Question 19

What do global reactions relate?

Answer 19

These are balanced reactions that correctly relate moles of reactant to moles of product

Question 20

What are two ways in which you can observe an elementary reaction in the labratory?

Answer 20

REMPI-MS (Resonance-enhanced multiphoton ionization mass spectrometry)
LI-TOF-MS (Laser-ionization time-of-flight mass spectrometry)

Question 21

Why can you only observe elementary reactions in complex lab procedures?

Answer 21

They involve unstable reactive intermediates like OH radicals that drive flame chemistry but cannot be isolated as stable species

Question 22

What are the ways to observe Global reactions?

Answer 22

gas chromatography (gc), liquid chromatography (lc) or spectroscopy

Question 23

What do you plot to analyze a Global reaction?

Answer 23

concentration as a function of time, then fit the data to a rate law

Question 24

What does the graph of zero order look like?

Answer 24

negative linear slope

Question 25

What does the graph of first order look like?

Answer 25

positive linear slope starting at 0,0

Question 26

What does the graph of third-order look like?

Answer 26

negative slope with a slight curve downward