Rates of Reaction and Equilibrium

Question 1

Define ‘rate of reaction’

Answer 1

The change in concentration of a reactant or product in a given time

Question 2

What 4 factors change the rate of a chemical reaction?

Answer 2

Concentration
Temperature
Use of catalyst
Surface area of solid reactants

Question 3

What two conditions have to be met for a successful collision?

Answer 3

Particles collide with correct orientation

Particles have sufficient energy to overcome the activation energy barrier of a reaction

Question 4

Explain the effect of increasing concentration of a reactant

Answer 4

Increased concentration increases number of particles in the same volume
Particles are closer together
Particles collide more frequently
More successful collisions so greater rate of reaction

Question 5

Explain the effect of increasing pressure of a gas on rate of reaction

Answer 5

Concentration of molecules occupies smaller volume
Gas molecules are closer together
Collide more frequently
More effective collisions
Increased rate of reaction

Question 6

What two ways can the progress of a reaction be followed?

Answer 6

Monitoring removal of a reactant

Following formation of a product

Question 7

What 3 measurable things may change during a reaction?

Answer 7

Gas volume
Mass of reactants or products
Colour

Question 8

What two methods can be used to determine rate of reaction if a gas is involved?

Answer 8

Volume of gas produced

Monitoring loss of mass of reactants using a balance

Question 9

What is a catalyst?

Answer 9

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

Question 10

How does a catalyst increase rate of reaction?

Answer 10

Provides an alternative pathway of lower activation energy

Question 11

What is a homogenous catalyst?

Answer 11

A catalyst that has the same physical state as the reactants.

Question 12

How does a homogenous catalyst work?

Answer 12

Catalyst reacts with reactants to form intermediates

Intermediate then breaks down to form product and regenerates the catalyst

Question 13

Give 2 examples of where homogenous catalysis is used

Answer 13

Making esters with a sulfuric acid catalyst

Ozone depletion

Question 14

What is a heterogenous catalyst?

Answer 14

A catalyst that has a different physical state from the reactants

Question 15

How does a heterogenous catalyst work?

Answer 15

Reactant molecules are adsorbed onto the surface of catalyst
Reaction takes place
Product molecules leave surface of catalyst by desorption

Question 16

Give 3 common processes where heterogenous catalysis is used

Answer 16

Making ammonia
Reforming
Hydrogenation of alkenes

Question 17

What are 3 key features of a Boltzmann distribution curve?

Answer 17

No molecules have 0 energy
Area under curve is equal to total number of molecules
No maximum energy for a molecule

Question 18

What happens to a Boltzmann distribution curve with an increased in temperature?

Answer 18

Peak shifts right and down

Question 19

What happens at a higher temperature to the molecules according to Boltzmann distribution?

Answer 19

More molecules have energy greater than or equal to activation energy
Greater proportion of collisions leads to a reaction
Collisions will be more frequent, but increased energy is more important

Question 20

Describe the effect of a catalyst on the Boltzmann distribution curve

Answer 20

Shifts Ea to the left so greater proportion of molecules have energy levels greater than or equal to that of the activation energy

Question 21

What are the two key features of an equilibrium system?

Answer 21

The rate of the forward reaction is equal to that of the reverse reaction
Concentrations of reactants and products do not change

Question 22

How does a reaction remain in equilibrium?

Answer 22

By being a closed system

Question 23

What does Le Chatelier’s principle state?

Answer 23

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

Question 24

Explain the importance of catalysts on sustainability

Answer 24

Increased sustainability by lowering temperature demands and reducing energy demands of fossil fuels with resulting reductions in carbon dioxide emissions

Question 25

What does an increase in temperature do to to the equilibrium position?

Answer 25

Shifts it in the endothermic direction

Question 26

What does a decrease in temperature do to to the equilibrium position?

Answer 26

Shifts in the exothermic direction

Question 27

What does an increase in pressure do to to the equilibrium position?

Answer 27

Shifts it to the side with fewer gas molecules

Question 28

What does a decrease in pressure do to to the equilibrium position?

Answer 28

Shifts it to the side with greater number gas molecules

Question 29

What is the effect of a catalyst on equilibrium position?

Answer 29

Doesn’t change position

Speeds up rate of forward and reverse equally

Question 30

What does a Kc value of 1 indicate?

Answer 30

The position of equilibrium is halfway between reactants and products

Question 31

What does a Kc value > 1 indicate?

Answer 31

Position of equilibrium is towards the products

Question 32

What does a Kc value of < 1 indicate?

Answer 32

A position of equilibrium that is towards reactants