Chapter 17

Question 1

What allows ions or molecules to overcome repulsive forces and react?

Answer 1

Very high kinetic energy.

Question 2

Do chemical equations indicate the reaction mechanism?

Answer 2

No.

Question 3

What is a reaction mechanism?

Answer 3

A step-by-step sequence of reactions leading to a chemical change.

Question 4

What must the steps in a reaction mechanism do?

Answer 4

Add up to give the overall equation.

Question 5

How is the sequence of steps in a reaction mechanism determined?

Answer 5

Through experiments.

Question 6

What are intermediates in a reaction mechanism?

Answer 6

Species that appear in some steps but not in the net equation.

Question 7

What is a homogeneous reaction?

Answer 7

A reaction where reactants and products are in a single phase.

Question 8

What must reactant molecules do for a reaction to occur?

Answer 8

Collide with favorable orientation and sufficient energy.

Question 9

What is collision theory?

Answer 9

The set of assumptions regarding collisions and reactions.

Question 10

Is the formation of water from oxygen and hydrogen exothermic or endothermic?

Answer 10

Exothermic.

Question 11

Does the formation of water from oxygen and hydrogen occur spontaneously at room temperature?

Answer 11

No.

Question 12

What must happen for new bonds to be formed in a reaction?

Answer 12

It must have sufficient energy and favorable orientation.

Question 13

Is bond breaking endothermic or exothermic?

Answer 13

Endothermic.

Question 14

Is bond forming endothermic or exothermic?

Answer 14

Exothermic.

Question 15

What does the initial energy input do in a reaction?

Answer 15

It overcomes repulsion forces and activates the reaction.

Question 16

What is activation energy (Ea)?

Answer 16

The minimum energy required to activate a reaction and form an activated complex.

Question 17

What happens when molecules collide with high kinetic energy?

Answer 17

Some energy is converted into internal potential energy, activating the molecules.

Question 18

What is an activated complex?

Answer 18

A transitional structure formed during a collision, where old bonds break and new bonds form.

Question 19

What happens to bonds in the activated complexes for the forward and reverse reactions?

Answer 19

A bond broken in the forward reaction’s activated complex must be reformed in the reverse reaction’s activated complex.

Question 20

Where do activated complexes occur along the reaction pathway?

Answer 20

At the high energy positions.

Question 21

According to the KMT, what happens as the temperature increases?

Answer 21

The speed and kinetic energy of molecules increase, leading to more collisions and more reactions.

Question 22

How does raising the temperature affect the reaction rate?

Answer 22

It provides more molecules with the necessary activation energy, increasing the reaction rate.

Question 23

What is the reaction rate?

Answer 23

The change in concentration of reactants as a reaction proceeds.

Question 24

What is chemical kinetics?

Answer 24

The area of chemistry concerned with reaction rates and mechanisms.

Question 25

What must particles do for reactions (other than simple decompositions) to occur?

Answer 25

They must have sufficient energy and favorable orientation.

Question 26

What does the rate of a reaction depend on?

Answer 26

The collision frequency and collision efficiency of the reactants.

Question 27

What are the rate influencing factors?

Answer 27

1) Nature of reactants 2) Surface area 3) Temperature 4) Concentration 5) Prescence of catalysts

Question 28

How is the nature of reactants a rate-influencing factor?

Answer 28

It affects the reaction rate based on the type of reactants and bonds involved.

Question 29

How is temperature a rate-influencing factor?

Answer 29

Higher temperature increases the speed and kinetic energy of particles, leading to more collisions and a faster reaction rate.

Question 30

How is surface area a rate-influencing factor?

Answer 30

A larger surface area allows for more collisions, increasing the reaction rate.

Question 31

How is concentration a rate-influencing factor?

Answer 31

Higher concentration increases the number of reactant particles, leading to more collisions and a faster reaction rate.

Question 32

How is the presence of catalysts a rate-influencing factor?

Answer 32

Catalysts lower the activation energy, increasing the reaction rate without being consumed.

Question 33

How does concentration affect reaction rates in homogeneous reaction systems?

Answer 33

Higher reactant concentration increases the reaction rate.

Question 34

What is catalysis?

Answer 34

The action of a catalyst.

Question 35

How does a catalyst affect a reaction?

Answer 35

It provides a pathway with a lower activation energy.

Question 36

How does a catalyst lower activation energy?

Answer 36

By forming an alternative activated complex.

Question 37

Do catalysts appear in the final products of a reaction?

Answer 37

No, they accelerate the reaction without being consumed.

Question 38

What is a homogeneous catalyst?

Answer 38

A catalyst in the same phase as the reactants and products.

Question 39

What is a heterogeneous catalyst?

Answer 39

A catalyst in a different phase than the reactants.

Question 40

What is often used as a heterogeneous catalyst?

Answer 40

Metals.

Question 41

How is the relationship between reaction rate and reactant concentration determined?

Answer 41

Experimentally, through a series of tests.

Question 42

What is a rate law?

Answer 42

An equation that relates reaction rate to reactant concentrations for a specific reaction at a given temperature.

Question 43

How does doubling the concentration affect a first-order reaction?

Answer 43

The reaction rate doubles.

Question 44

How does doubling the concentration affect a second-order reaction?

Answer 44

The reaction rate quadruples.

Question 45

How does doubling the concentration affect a zero-order reaction?

Answer 45

The reaction rate stays the same.

Question 46

How does the reaction rate change with [H₂] in the given reaction?

Answer 46

It is directly proportional; doubling [H₂] doubles the rate, tripling [H₂] triples the rate.

Question 47

How does the reaction rate change with [NO] in the given reaction?

Answer 47

It increases fourfold when [NO] is doubled and ninefold when [NO] is tripled.

Question 48

What is the overall rate law for the reaction 2H₂(g) + 2NO(g) → N₂(g) + 2H₂O(g)?

Answer 48

R = k[H₂][NO]²

Question 49

What happens to the rate constant (k) as temperature increases?

Answer 49

The value of k usually increases, but the relationship between reaction rate and concentration remains unchanged.

Question 50

What is the overall order of a reaction?

Answer 50

The sum of all reactant orders in the rate law.

Question 51

Do the orders in the rate law always match the coefficients in the balanced equation?

Answer 51

No, they must be determined experimentally.

Question 52

What is the specific rate constant (k)?

Answer 52

The proportionality constant relating reaction rate to reactant concentrations.

Question 53

How is the value of k determined?

Answer 53

Experimentally, after determining the reaction orders.

Question 54

Does k have the same value for different reactions?

Answer 54

No, k is specific to each reaction, even under the same conditions.

Question 55

What do the units of k depend on?

Answer 55

The overall order of the reaction.

Question 56

Does k change with reactant or product concentrations?

Answer 56

No, k remains constant throughout the reaction and does not change with time.

Question 57

How does temperature affect k?

Answer 57

Increasing temperature increases the value of k.

Question 58

How does a catalyst affect k?

Answer 58

A catalyst increases the value of k.

Question 59

How is the rate law determined for a single-step reaction?

Answer 59

It is proportional to the product of reactant concentrations, each raised to its stoichiometric coefficient.

Question 60

How is the rate law determined for multi-step reactions?

Answer 60

It is based on the slowest step, called the rate-determining step.