Chapter 10 - Reaction rates and Equilibrium

Question 1

Define Activation Energy

Answer 1

The minimum energy required to start a reaction by the breaking of bonds

Question 2

What does rate of reaction measure (2)

Answer 2

How fast a reactant is being used up
or
how fast a product is being formed

Question 3

What features can affect rate of reaction?

Answer 3

Concentration or pressure
Temperature
Use of a catalyst
Surface area of solid reactants

Question 4

What does the collision theory state?

Answer 4

That 2 reacting particles must collide for a reaction to occur.

Question 5

What are the 2 conditions reacting particles have to meet for a successful collision?

Answer 5

The particles have sufficient energy to overcome the activation energy barrier of the reaction
The particles collide with the correct orientation

Question 6

What is the equation for rate of reaction?

Answer 6

Rate (moldm-3s-1) = change in concentration (moldm-3)/

Time (s)

Question 7

What happens to rate of reaction when the concentration of a reactant is increased? Why?

Answer 7

The rate increases because the number of particles in the same volume increases and therefore particles are closer together and will collide more frequently. In a given time there will therefore be more effective collisions and the rate of reaction will increase

Question 8

What happens to rate of reaction when the pressure of a reactant is increased? Why?

Answer 8

The rate increases because the same number of particles are compressed into a smaller volume and therefore particles are closer together and will collide more frequently. In a given time there will therefore be more effective collisions and the rate of reaction will increase

Question 9

What are the 2 methods for following the progress of a reactiopn?

Answer 9

Monitoring the removal of a reactant (decease in concentration)
Monitoring the formation of a product (increase in concentration)

Question 10

What is one method of determining rate of reaction for a reaction that produces gases?

How would you record this data?

Answer 10

Monitoring the volume of gas produced at regular intervals by collecting the gases formed.
Use a water trough and an upside down measuring cylinder filled with water, connected to a conical flask where the reaction is taking place by a delivery tube to measure the gas formed.
Time(x) against volume of gas produced (y)

Question 11

What is another method of determining rate of reaction for a reaction that produces gases?

How would you record this data?

Answer 11

Monitor the mass loss of the reactant using a balance. 
Mass lost (y) against time (x)

Question 12

What is a catalyst and what does it do?

Answer 12

A catalyst is a substance that changes the rate of reaction without undergoing any permanent change itself

Question 13

How does a catalyst increase the rate of reaction?

Answer 13

It provides an alternative reaction pathway with a lower activation energy

Question 14

What are the types of catalysts?

Answer 14

Homogeneous

Heterogeneous

Question 15

What is a homogeneous catalyst? What does it do?

Answer 15

A catalyst with the same physical state as the reactants. It reacts with the reactants to form an intermediate which then breaks down to give the products and regenerates the catalyst

Question 16

What are homogeneous catalysts used for? (2) and in each case what is the catalyst

Answer 16

Making esters - sulfuric acid

Ozone depletion - Cl radicals

Question 17

What is a heterogeneous catalyst and what does it do?

Answer 17

It is a catalyst that has a different physical state to the reactants. The reactant molecules are weakly bonded (adsorbed) onto the surface of the catalyst where a reaction occurs. The product molecules are then desorbed from the catalyst. The catalyst is usually a solid in contact with gaseous or aqueous reactants

Question 18

What are heterogeneous catalysts used for? (2) and in each case what is the catalyst

Answer 18

Making ammonia via the haber process - solid Iron

Hydrogenation of alkenes Ni(s)

Question 19

What are the positives to the use of catalysts? (4)

Answer 19

Lower production costs as temperatures requirements are reduced
More products can be produced more quickly using less energy - increases profitability
It lowers the temperatures, reducing the demand for fossil fuels so less CO2 is emitted
Better atom economy (reduces wastage and pollutants

Question 20

What are the negatives to the use of catalysts? (4)

Answer 20

Some catalysts are toxic so need to be disposed of carefully
Catalysts can be very specific and only catalyse one reaction
Catalysts can be very expensive
Some catalysts are poisoned by impurities and will become inefficient over time

Question 21

What does the Maxwell Boltzmann distribution graph show?

Answer 21

The energy distribution of all molecules in a gaseous state

Question 22

Describe the basics of a Maxwell Boltzmann distribution graph

Answer 22

The number of molecules is on the Y axis
The energy is on the X axis
The activation energy is represented by a vertical line coming up from the energy

Question 23

Where does the curve start on a Maxwell Boltzmann distribution graph?

Answer 23

At the origin (0,0)

Question 24

What does the area under the Maxwell Boltzmann distribution graph give?

Answer 24

The total number of molecules

Question 25

What does the peak on the Maxwell Boltzmann distribution graph show?

Answer 25

The most likely energy of any molecule

Question 26

What happens if you use a catalyst in a reaction and how is this shown on a Maxwell Boltzmann distribution graph?

Answer 26

Provides an alternative energy pathway which lowers the activation energy which means more molecules have sufficient energy to react when they collide. This is represented as a vertical line from the X axis but is a smaller energy and is therefore closer to the y axis than the activation energy without a catalyst

Question 27

At a higher temperature what happens to the most likely energy of any molecule?

Answer 27

It will increase (meaning the peak will be further from the Y axis at a higher energy)

Question 28

What happens to the area of the Maxwell Boltzmann distribution graph when the temperature increases?

Answer 28

It remains the same because no new molecules have been introduced

Question 29

When at a higher temperature what happens to the number of molecules that have energy equal to or greater than the activation energy?

Answer 29

It increases because molecules have more energy

Question 30

What happens to the number of collisions at a higher temperature?

Answer 30

It increases in frequency because the molecules have more energy and will collide more often due to moving more

Question 31

What happens to the rate of reaction at higher temperatures?

Answer 31

It INCREASES due to an increase in energy of molecules and an increase in the frequency of collisions

Question 32

What conditions are required for dynamic equilibrium to be achieved?

Answer 32

Closed system with a reversible reaction

Question 33

Define closed system

Answer 33

A system where reactants and products are isolated from their surroundings so their temperature, pressure and concentrations remain unaffected by outside influences.

Question 34

Define dynamic equilibrium

Answer 34

exists in a closes system where the rate of the forwards reaction is equal to the rate of the reverse reaction and the concentrations of the products and reactants has not changed

Question 35

List 4 features of dynamic equilibrium

Answer 35

the concentrations of the products and reactants does not change the rate of the forward reaction equals the rate of the backwards reaction it is in a closed sytem there is no change in macroscopic properties

Question 36

What 3 physical changes can be predicted by Le Chatelier's principle?

Answer 36

Change in temperature Change in pressure Change in concentration

Question 37

What does Le Chatelier's principle state?

Answer 37

when a system in equilibrium is subjected to an external change the system readjusts itself to minimise the effect of that change

Question 38

What happens to the position of equilibrium if the concentration of a product is increased?

Answer 38

The equilibrium will shift to the left to form more reactants

Question 39

What happens to the position of equilibrium if the concentration of a reactant is increased?

Answer 39

The equilibrium will shift to the right to form more products

Question 40

What happens to the equilibrium if pressure is increased?

Answer 40

Equilibrium shifts to the side with fewer molecules

Question 41

What happens to the position of equilibrium if pressure is decreased?

Answer 41

Equilibrium shifts to the side with more molecules

Question 42

What happens to the position of equilibrium if pressure is increased or decreased in a reaction which has the same number of molecules on both sides?

Answer 42

There will be no effect on the position of equilibrium because there are the same number of molecules on either side

Question 43

What happens to the position of equilibrium if temperature is decreased in a exothermic reaction?

Answer 43

It shift to the exothermic side which is the product side

Question 44

What happens to the position of equilibrium if temperature is increased in an exothermic reaction?

Answer 44

It shift to the endothermic side which is the reactant side

Question 45

What happens if the position of equilibrium if temperature is increased in an endothermic reaction?

Answer 45

It shift to the endothermic side which is the product side

Question 46

What happens to the position of equilibrium if temperature is decreased in an endothermic reaction?

Answer 46

It shift to the side exothermic side which is the reactant side

Question 47

Do catalysts affect the position of equilibrium?

Answer 47

No but it increases the rate of the forwards and reverse reaction equally.

Question 48

How can the position of equilibrium be calculated?

Answer 48

Using the equilibrium law where you use the concentrations of products and reactants at equilibrium

Question 49

If the value of equilibrium constant is 1 what does it mean about the position of equilibrium?

Answer 49

It is halfway between the products and reactants

Question 50

If the value of equilibrium constant is less than 1 what does it mean about the position of equilibrium?

Answer 50

It is towards the reactant side

Question 51

If the value of equilibrium constant is more than 1 what does it mean about the position of equilibrium?

Answer 51

It is towards the product side

Question 52

What is an equilibrium constant?

Answer 52

The actual position of equilibrium