Topic 9: Kinetics I

Question 1

What theory explains how chemical reactions occur when particles collide?

Answer 1

Collision theory

It describes the conditions required for a successful reaction.

Question 2

What is the minimum energy required for a reaction to occur when particles collide?

Answer 2

Activation energy

Represented by Ea.

Question 3

True or False:

Every collision between particles results in a chemical reaction.

Answer 3

False

Only collisions with enough energy and correct orientation react.

Question 4

Why do most collisions between particles not lead to a reaction?

Answer 4

Insufficient energy

Many particles do not reach the activation energy.

Question 5

What must particles have during a collision for a reaction to occur?

Answer 5

Energy greater than activation energy.

This allows bonds to break and new ones to form.

Question 6

Fill in the blank:

Collisions that lead to reactions are called _______ collisions.

Answer 6

successful

These result in product formation.

Question 7

What happens to bonds in reactant molecules when activation energy is supplied?

Answer 7

Bonds break

This allows atoms to rearrange to form products.

Question 8

True or False:

Increasing the energy of colliding particles increases the chance of a successful collision.

Answer 8

True

More particles exceed the activation energy threshold.

Question 9

What two conditions must be met for a collision to result in a reaction?

Answer 9

1. Sufficient energy
2. Correct orientation

Both are required for a successful collision.

Question 10

What distribution describes the range of energies possessed by molecules in a gas?

Answer 10

Maxwell–Boltzmann distribution

Shows how many particles have a given kinetic energy.

Question 11

Fill in the blank:

The Maxwell–Boltzmann distribution shows the spread of _______ energies of particles.

Answer 11

kinetic

Not all particles have the same energy.

Question 12

What does the area under a Maxwell–Boltzmann distribution curve represent?

Answer 12

Total number of particles

The total remains constant at a given sample size.

Question 13

True or False:

All particles in a gas have the same kinetic energy.

Answer 13

False

Energies are distributed over a wide range.

Question 14

On a Maxwell–Boltzmann graph, what does the x-axis represent?

Answer 14

Kinetic energy

Sometimes labelled as energy of particles.

Question 15

On a Maxwell–Boltzmann graph, what does the y-axis represent?

Answer 15

Number of molecules

Indicates how many particles have a certain energy.

Question 16

Fill in the blank:

Increasing temperature shifts the Maxwell–Boltzmann curve to the _______.

Answer 16

right

More particles have higher energies.

Question 17

What happens to the peak height of the distribution curve when temperature increases?

Answer 17

decreases

The curve becomes broader and flatter.

Question 18

True or False:

Increasing temperature increases the proportion of particles with energy greater than activation energy.

Answer 18

True

This increases reaction rate.

Question 19

What part of the Maxwell–Boltzmann curve represents particles with enough energy to react?

Answer 19

Area beyond activation energy

These particles can undergo successful collisions.

Question 20

Fill in the blank:

The vertical line often drawn on a Maxwell–Boltzmann graph represents the _______ energy.

Answer 20

activation

Only particles beyond this line can react.

Question 21

Why does increasing temperature increase the rate of reaction according to the distribution?

Answer 21

More particles exceed activation energy

A greater fraction of collisions become successful.

Question 22

What term describes how fast reactants are converted into products in a chemical reaction?

Answer 22

Rate of reaction

Usually measured as change in concentration over time.

Question 23

Fill in the blank:

Rate of reaction describes the _______ of a chemical reaction.

Answer 23

speed

Faster reactions produce products more quickly.

Question 24

True or False:

Increasing temperature generally increases the rate of reaction.

Answer 24

True

Particles move faster and collide more frequently.

Question 25

What happens to the **average kinetic energy** of particles when **temperature increases**?

Answer 25

It **increases**. ## Footnote Particles move faster at higher temperatures.

Question 26

How does **increasing temperature** affect the **frequency of collisions between particles**?

Answer 26

It increases collision frequency. ## Footnote Faster particles collide more often.

Question 27

# Fill in the blank: Increasing **temperature** increases the proportion of particles with energy greater than the _\_\_\_\_\_\_ energy.

Answer 27

activation ## Footnote More particles can undergo successful collisions.

Question 28

Why does a **small temperature increase** often cause a **large increase in reaction rate**?

Answer 28

Many more particles exceed activation energy. ## Footnote The high-energy tail of the distribution increases significantly.

Question 29

# True or False: Increasing **temperature** changes the **activation energy of a reaction**.

Answer 29

False ## Footnote Activation energy remains constant unless a catalyst is used.

Question 30

What **two factors** increase when **temperature rises according to collision theory**?

Answer 30

* Collision frequency * Energy ## Footnote Both increase the likelihood of successful collisions.

Question 31

What **experimental reaction** is commonly used to study the **effect of temperature on reaction rate in the laboratory**?

Answer 31

Sodium thiosulfate and hydrochloric acid. ## Footnote The reaction produces sulfur which clouds the solution.

Question 32

# Fill in the blank: In **rate experiments**, rate is often measured as the _\_\_\_\_\_\_ in **concentration per unit time**.

Answer 32

change ## Footnote For example mol dm⁻³ s⁻¹.

Question 33

Why does **increasing temperature** make **collisions more likely to be successful**?

Answer 33

More particles exceed activation energy. ## Footnote Therefore a larger fraction of collisions lead to reaction.

Question 34

How does **increasing concentration** affect the **rate of a reaction**?

Answer 34

It increases the rate. ## Footnote More particles are present in a given volume.

Question 35

# Fill in the blank: Increasing **concentration** increases the _\_\_\_\_\_\_ of **collisions between particles**.

Answer 35

frequency ## Footnote More particles lead to more frequent collisions.

Question 36

# True or False: Decreasing concentration usually **decreases the rate of reaction**.

Answer 36

True ## Footnote Fewer particles collide per unit time.

Question 37

What is the effect of **increasing the pressure of a gas** on reaction rate?

Answer 37

It increases the rate. ## Footnote Gas particles are closer together.

Question 38

# Fill in the blank: Increasing **gas pressure** decreases the _\_\_\_\_\_\_ between **gas particles**.

Answer 38

distance ## Footnote This increases collision frequency.

Question 39

Why does **increasing pressure** increase the **rate of reactions involving gases**?

Answer 39

Particles collide more often. ## Footnote The same number of particles occupy a smaller volume.

Question 40

# True or False: Changing **pressure** affects the **rate of reactions involving gases but not solids**.

Answer 40

True ## Footnote Solids are not significantly compressed by pressure changes.

Question 41

What **key factor in collision theory** is affected by changes in **concentration or pressure**?

Answer 41

Collision frequency ## Footnote More collisions increase the chance of successful reactions.

Question 42

What **experimental reaction** is used to investigate the **effect of concentration on rate**?

Answer 42

Reaction of calcium carbonate with hydrochloric acid. ## Footnote Produces and measures carbon dioxide gas.

Question 43

# True or False: Increasing **concentration** increases the **activation energy of a reaction**.

Answer 43

False ## Footnote Activation energy remains unchanged.

Question 44

What is a substance that **increases the rate of a chemical reaction** without being used up?

Answer 44

Catalyst ## Footnote It remains chemically unchanged at the end of the reaction.

Question 45

# Fill in the blanks: A **catalyst** increases reaction rate without changing its \_\_\_\_\_\_\_ or \_\_\_\_\_\_\_.

Answer 45

composition; amount ## Footnote It is not consumed during the reaction.

Question 46

# True or False: A **catalyst** is permanently used up during a reaction.

Answer 46

False ## Footnote Catalysts are regenerated by the end of the reaction.

Question 47

How does a **catalyst** increase the **rate of a reaction**?

Answer 47

Lowers activation energy. ## Footnote Provides an alternative reaction pathway.

Question 48

# Fill in the blank: **Catalysts** provide an **alternative reaction route** with _\_\_\_\_\_\_ activation energy.

Answer 48

lower ## Footnote More particles can react successfully.

Question 49

What effect does a **catalyst** have on the **Maxwell–Boltzmann distribution curve**?

Answer 49

No change to the distribution. ## Footnote The energy distribution remains the same.

Question 50

How does a **catalyst** increase the **proportion of successful collisions**?

Answer 50

It lowers the activation energy threshold. ## Footnote More particles exceed the required energy.

Question 51

# True or False: A **catalyst** increases the **kinetic energy of particles**.

Answer 51

False ## Footnote It lowers activation energy instead.

Question 52

On a **Maxwell–Boltzmann diagram**, how is the **effect of a catalyst** usually shown?

Answer 52

Activation energy line shifts left. ## Footnote The curve stays the same but Ea decreases.

Question 53

# Fill in the blank: Because **activation energy is lower**, a greater _\_\_\_\_\_\_ of particles have sufficient energy to react.

Answer 53

proportion ## Footnote This increases reaction rate.

Question 54

Why does **lowering activation energy** increase the **rate of reaction**?

Answer 54

More successful collisions occur. ## Footnote More collisions have enough energy to react.

Question 55

# True or False: Catalysts change the **overall enthalpy change** of a reaction.

Answer 55

False ## Footnote They only change the reaction pathway.