Arrhenius Theory and Catalysts

Question 1

Why does the rate of reaction depend on the activation energy?

Answer 1

o The rate of a reaction depends on the height of the barrier (the activation energy) because only a small fraction of the number of molecules at a given temperature have a sufficient energy to get over the barrier

Question 2

Describe the plot of the Arrhenius Equation

Answer 2

 If one constructs a plot of ln k vs 1/T the slope of the plot will be -Ea/R and the intercept will be ln A

Question 3

What is catalyst?

Answer 3

o A catalyst is a substance that speeds up the rate of a chemical reaction but is not consumed during the course of the reaction

Question 4

What is the transition state of interest?

Answer 4

 The transition state of interest for a given reaction is the highest energy point along the lowest energy path

Question 5

What is Catalysis?

Answer 5

o Catalysis is the lowering of the energy barrier to speed up a reaction

Question 6

What is the activation energy?

Answer 6

 The height of a barrier along the reaction pathway is the activation energy

Question 7

What is the mechanism of an enzyme?

Answer 7

Substrate + Enzyme Complex -> Product

Question 8

What are enzymes?

Answer 8

o Enzymes are biological catalysts
 They are proteins that fold into particular conformations such that they can help speed up very particular chemical reactions

Question 9

What is a reaction coordinate?

Answer 9

o A reaction coordinate is a path that links the reactant molecules and the products molecules

Question 10

What are the two types of catalysts?

Answer 10

o Catalysts in the same phase as the chemical reactants are called homogeneous catalysts, while those in different phases are called heterogeneous catalysts

Question 11

Where do intermediates lie on a reaction coordinate?

Answer 11

o Any minima that exist between the reactants and the products along the reaction coordinate are intermediates

Question 12

What is the Boltzmann distribution?

Answer 12

at a given temperature there is a distribution of kinetic energies for all the molecules in a sample

Question 13

What is the transition state?

Answer 13

 The transition state is the high energy point between two minima along the reaction coordinate

Question 14

Where does the substrate bind to the enzyme?

Answer 14

at the active site

Question 15

What is the pre-exponential factor?

Answer 15

• The pre-exponential factor is the ultimate rate of the reaction; it is the fastest the reaction could ever proceed (if barrier were zero or the temperature were infinite)

Question 16

How does a catalyst work? (3)

Answer 16

o They provide a means for the reactant molecules to break bonds and then form temporary bonds with the catalyst
o Some catalysts change during the course of the chemical reaction, but are then returned to their original state at the end of the reaction
o Catalysts can also function by “holding” molecules in particular configuration while simultaneously weakening some particular bonds
 This allows the catalyst to essentially “help” the chemistry by arranging the reactants in favorable geometries as well as by weakening bonds that need to break along the reaction coordinate

Question 17

What is Arrhenius Law?

Answer 17

o Arrhenius Law states that the rate of a reaction can be increased by increasing the temperature