Chapter 10 Rates and Equilibrium I

Question 1

What is the rate of a chemical reaction?

Answer 1

How quickly the products are formed/ the reactants are used up
Rate= Change in concentration/ Time moldm-3s-1

Question 2

When is the rate of a general reaction fastest and why?

Answer 2

At the beginning
Concentration of the reactants in highest, lots of particles in a given volume, more successful collisions in a given time, increasing rate of reaction

Question 3

What does collision theory state- general ?

Answer 3

For a reaction to occur, two reacting particles must collide

Question 4

What makes an effective collision?

Answer 4

Colliding particles have the correct orientation and sufficient energy to overcome the activation energy

Question 5

How does concentration affect rate of reaction?

Answer 5

Increasing concentration increases the number molecules in a given volume
Increases collision frequency, increasing the number of successful collisions, thus increasing rate of reaction

Question 6

How does pressure affect rate of reaction?

Answer 6

Increasing pressure increases the number molecules in a given volume
Increases collision frequency, increasing the number of successful collisions, thus increasing rate of reaction

Question 7

What are the two methods of measuring rate of reaction when a gas is produced?

Answer 7

Collect a volume gas
Measure loss of mass from reactants

Question 8

What is a catalyst?

Answer 8

A substance which increases the rate of a chemical reaction without being used up, by reducing the activation energy

Question 9

How does a catalyst work? How does this increase rate of reaction?

Answer 9

Provide an alternative reaction pathway with a lower activation energy
A greater proportion of these particles have the new lower Ea, increasing the number of effective collisions thus increasing rate of reaction

Question 10

What is a heterogeneous catalyst and how does it lower activation energy?

Answer 10

The catalyst is a different physical state to the reactants, providing a reaction surface

Reactant particles adsorbed (weakly bond) to the catalyst surface. Reaction occurs.
Products undergo desorption from the catalyst

Question 11

What is a homogeneous catalyst and how does it lower activation energy?

Answer 11

The catalyst is the same physical state physical state as the reactants
React to form an intermediate, which then goes on to react to reform the catalyst

Question 12

Give an example of a homogeneous and heterogeneous catalyst

Answer 12

Heterogeneous- Fe in the Haber Process
Homogeneous- Concentrated sulphuric acid in esterification

Question 13

LOOK AT ENERGY PROFILE DIAGRAMS

Answer 13

LOOK AT ENERGY PROFILE DIAGRAMS

Question 14

How do catalysts make processes more sustainable?

Answer 14

Catalysts are not used up
A lower temperature and pressure is needed as the rate of reaction is high enough
Therefore, there is a lower energy demand, reducing the need for burning fossil fuels
Products are formed at a higher rate making the process more profitable
Also less CO2 produced

Question 15

What are elastic collisions?

Answer 15

Collisions which do not result in the loss of energy, so particles do not slow down e.g with container walls

Question 16

What is the most common energy on the Boltzmann graph? What is the average kinetic energy and why?
What are the axis?

Answer 16

The peak
To the right of the peak as the graph is positively skewed
X= Energy, Y=Number of molecules at each energy

Question 17

Where does the boltzmann start and why? Where does it end and why? What does the area under it represent?

Answer 17

At 0 as no particles have 0 energy
Does not meet the x axis as no particle has an infinite energy
The total number of molecules of the sample

Question 18

How does temperature affect rate of reaction? How does it affect the boltzmann graph?

Answer 18

Graph to the right but peak slightly lower so the area of the graph is constant
Increases the average kinetic energy of the particles, a greater proportion of particle have energy to overcome the activation energy
Increases the proportion of collisions which are successful, increasing successful collision frequency so increases rate of reaction
(lower effect, increase speed of particles, so collide more frequently)

Question 19

What is a reversible reaction?

Answer 19

A reaction where the products can react to form the reactants

Question 20

What are the features of dynamic equilibrium?

Answer 20

The rate of the forward reaction is equal to the rate of the backward reaction
The concentration of the reactants and the products is constant
Must be a closed system

Question 21

What is Le Chatelier’s principle?

Answer 21

The principle which states that if a change is made to a system in equilibrium, the system will move to oppose the change
e.g raise temp, used up excess heat with endothermic reaction

Question 22

How would an increase in the reactants affect the position of equilibrium?

Answer 22

To the right
Greater concentration of reactants, increases rate of forward to minimise addition, to the right

Question 23

How would a decrease in concentration of the reactants affect the position of equilibrium?

Answer 23

To the left
Fewer reactants, to minimise, increase rate of backward to minimise loss, pushing to the left

Question 24

How would a decrease in temperature affect the position of the reaction? e.g forward exothermic

Answer 24

To the right here
Add heat to minimise removal by increasing exothermic reactions, so moves the position to the other side, so right

Question 25

How would an increase in pressure affect the position of equilibrium?

Answer 25

To the side with fewer gaseous moles
More compressed, moves to side where less space needed
If equal number of gaseous moles, no impact

Question 26

What is the equilibrium constant and the equation?

Answer 26

An equation to show the relative position of equilibrium

Concentration Products/ Concentration Reactants

To the power of the number of moles

Question 27

What do the Kc values tell us?

Answer 27

If Kc>1, towards products
If Kc=1, halfway
If Kc<1, towards reactants

Question 28

What are the advantages of measuring mass loss over gas production?

Answer 28

Pro-No loss of gas? No max amount, unlike gas syringe
Con-low mass changes, small

Question 29

Why would lower temperatures be better for the environment?

Answer 29

Lower energy demands so fewer fossil fuels burnt
Less CO2 emissions

Question 30

What should you ensure about volumes with a rate experiment?

Answer 30

Volumes need to be large enough
e.g if a solid is reacting with acid, need enough acid to dissolve/react
If you need a certain volume, use a lower conc e.g 6cm3 is too small