Chapter 10 - Reaction Rates And Equilibrium

Question 1

Define rate of reaction

Answer 1

Measures how fast a reaction is used up or how fast a product is being formed

Question 2

Calculate the rate of reaction

Answer 2

Rate = change in concentration / time

Question 3

Describe the general concentration-time graph

Answer 3

• rate is faster at the start, as reactants is at its highest concentration
• rate slows down the reaction as the reactants are being used up and their concentration decrease
• once one of the reactants has been completely reacted, the concentration stops changing
• rate of reaction is zero

Question 4

Affecting the rate of reaction:
•
•
•
•

Answer 4

• concentration
• temperature
• catalyst
• surface area

Question 5

What is the collision theory?

Answer 5

Two reacting particles must collide for a reaction to occur

Question 6

What two conditions have to be met for an effective collision?

Answer 6

• the particle collide with the correct orientation

* the particles have sufficient energy to overcome the Ea barrier of reaction

Question 7

How does the concentration affect the rate of reaction?

Answer 7

Increase concentration, increase rate of reaction due to increase number of particles in same volume. Particles are closer so frequently collide. More effective collisions.

Question 8

How does increasing the pressure of gas affect the rate of reaction?

Answer 8

Increasing pressure, increases rate of reaction as gas is in smaller volume the concentration increases. Frequent effective collisions

Question 9

How can you follow the progress of a reaction?

Answer 9

• monitoring the removal of a reactants

* following the formation of a product

Question 10

Two ways to determine the rate of reaction when a gas is formed?

Answer 10

• monitoring the volume of gas produced at regular time intervals (gas collections)
• monitoring the loss of mass of reactants using a balance

Question 11

Define a catalyst

Answer 11

A substance that changes the rate of reaction without undergoing permanent change

Question 12

What are the three main characteristics of a catalyst?

Answer 12

• catalyst is not used up in chemical reaction
• may react with a reactant to form an intermediated / provide a surface for the reaction to take place
• is regenerated at the end of a reaction

Question 13

Why does a catalyst increase the rate of reaction?

Answer 13

Provides an alternative reaction pathway of lower activation energy

Question 14

What are the two types of catalyst?

Answer 14

• homogeneous catalyst

* heterogeneous catalyst

Question 15

What is a homogeneous catalyst?

Answer 15

The same physical star as the reactants. The catalyst reacts to form an intermediate breaking down to give the product and regenerate the catalyst

Question 16

Define the intermediate

Answer 16

A species formed during a reaction that reacts further and is not present in the final products

Question 17

What is a heterogeneous catalyst?

Answer 17

Has a different physical state from the reactants. (Usually solid in contact with gaseous reactants).
Reactants are absorbed onto the surface of the catalyst where reaction takes place. Produces leave the the surface of the catalyst by desorption

Question 18

Why is a catalyst a sustainability and economic importance?

Answer 18

• increase rate of reaction - lowering Ea - reduces the temperature
• decreases expensive
• requires less fossil fuels - less pollutants - decreasing CO2

Question 19

What is the Boltzmann distribution showing if the graph?

Answer 19

Shows the number of molecules distributed to the molecules energy leaves

Question 20

What are the features shown on the boltzamann distribution?

Answer 20

• no molecules have zero energy - curve starts at the origin
• area under the curve = number of molecules
• no maximum energy for a molecule - curve doesn’t meet at x-axis at high energy

Question 21

Describe using Boltzmann distribution for a higher temperature

Answer 21

More molecules have an energy greater than or equal to Ea. Greater proportion of collision, increase rate of reactions. Collisions is more frequent as molecules are moving faster

Question 22

How does a catalyst affect the Boltzmann distribution?

Answer 22

Catalyst provides alternative tour with lower Ea. Using a catalysed means a greater proportion of molecules have energy greater or equal than the lower Ea. More molecules will react to form a product.

Question 23

What is a dynamic equilibrium ?

Answer 23

The rate of the forward and reverse reaction is the same. The concentrations of the reactants and products don’t change.

Question 24

Define Le Chateliers Principle

Answer 24

When a system I’m equilibrium is subjected to an external change the system readjusts itself minimise the effect of change

Question 25

What effect does the concentration change in a equilibrium?

Answer 25

Changing the concentration changes the rate of the forward/reverse reaction

Question 26

How does the equilibrium change if more products are formed?

Answer 26

Shifts to the right

Question 27

How does the equilibrium change if more reactants are formed?

Answer 27

Shifts to the left

Question 28

What does the shift in the equilibrium depend on if temperature change?

Answer 28

The sign of 🔺H

Question 29

Is the 🔺H positive or negative if an increase in temperature shifts the equilibrium position in the endothermic direction?

Answer 29

Positive

Question 30

Is the 🔺H positive or negative if an decreases in temperature shifts the equilibrium position in the exothermic direction?

Answer 30

Negative

Question 31

If the forward reaction is exothermic how does the increase temperature effect the equilibrium?

Answer 31

* position of equilibrium shifts to the left | * more reactants are made

Question 32

If the forward reaction is endothermic how does the increase temperature effect the equilibrium?

Answer 32

* position of equilibrium shifts to the right | * more products are made

Question 33

If the forward reaction is exothermic how does the decrease temperature effect the equilibrium?

Answer 33

* position of equilibrium shifts to the right | * more products are made

Question 34

If the forward reaction is endothermic how does the decrease temperature effect the equilibrium?

Answer 34

* position of equilibrium shifts to the left | * more reactants are made

Question 35

How does the increase in pressure effect the equilibrium?

Answer 35

Shifts the position of equilibrium to the side with fewer molecules (reducing the pressure of the system)

Question 36

How does a catalyst effect the equilibrium?

Answer 36

Doesn’t effect the change in position. Just speeds up the rate of reaction.

Question 37

The Haber process, what could be done to maximise the yield of ammonia?

Answer 37

* low temperature -> shifts to the right | * high pressure -> shifts to the right

Question 38

Why doesn’t the Haber process use this conditions to maximise yield?

Answer 38

* low temperature -> slow reaction * high temperature -> strong container needed + large quantities of water + increase costs + possible leaking of toxic hot gases

Question 39

What catalyst is used in the Haber process?

Answer 39

Iron

Question 40

What is a catalyst?

Answer 40

A substance that speeds up a reaction by providing an alternative route with a lower activation energy. At the end of the reaction, the catalyst is regenerated

Question 41

How would you measure the rate of reaction between calcium carbonate and hydrochloric acid?

Answer 41

Add the reactants to a conical flask, which is upon a balance Record the mass of the flask initially and at regular intervals The reaction is complete when no more mass is lost

Question 42

How would you work out the rate of reaction from a graph?

Answer 42

Draw a tangent against the curve and find the gradient Gradient = dy / dx This is the rate of reaction at that time

Question 43

How would you measure the rate of reaction of the decomposition of hydrogen peroxide?

Answer 43

Place the hydrogen peroxide in a conical flask attached to a gas syringe Add some manganese dioxide, which acts as a catalyst Record the volume of gas in the cylinder at regular intervals When no more gas is produced, the reaction has finished

Question 44

How does increasing the pressure of a gas increase the rate of reaction?

Answer 44

An increase in pressure means that volume decreases. There is, therefore, the same number of particles but in a smaller area, which means that they are closer together and successful collisions are more common

Question 45

How does increasing the concentration of particles increase the rate of reaction?

Answer 45

Increasing the concentration increases the number of particles in the same volume. This means that they are closer together and so will collide much more frequently, so there are more chances to react

Question 46

What are the two characteristics of a successful collision?

Answer 46

The particles collide with the correct orientation | They collide with sufficient energy