Chapter 10: Reaction rates and equilibrium

Question 1

What is rate of reaction?

Answer 1

The rate of a chemical reaction measures how fast a reaction is used up or how fast a product is being formed. It defined as the change in concentration of a react or a product in a given time.

Question 2

What is the rate equation?

Answer 2

Rate = change in concentration / time
mol dm-3 s-1 = mol dm-3 / s

Question 3

How does rate of reaction change with time?

Answer 3

• the rate of reaction is faster at start of the reaction, as each reactant is at its highest concentration
• the rate of reaction slows down as the exactions proceeds as reactant concentration is decreasing
• once the limiting reactant is used to the concentration stops changing and rate of reaction is zero.

Question 4

What factors can alter the rate of reaction?

Answer 4

• concentration
• temperature
• use of catalyst
• surface area of solid reactant

Question 5

what is collision theory?

Answer 5

Collision theory states that two reacting particles must collide with the correct orientation and enough energy for a reaction to take place.

Question 6

What is needed for a collision to be effective?

Answer 6

• the particles collide with the correct orientation
• the particle have sufficient energy to overcome the activation energy barrier of the reaction.

Question 7

How does the change in concentration affect rates of reaction?

Answer 7

When the concentration of a react is increased, the rate of reaction generally increases. An increase in concentration increase the amount of particles, making the closer together and therefor collide more frequently resulting in more succession collisions and increased rate of reaction.

Question 8

How does increases the pressure of a gas effect the rate of reaction?

Answer 8

When a gas is compressed into a smaller volume the pressure increased and rate of reaction increases. The concentration of the gas molecule increase the particles are closer together and collide more frequent ply leading to more effective collisions.

Question 9

How to measure the progress of a reaction?

Answer 9

• monitoring the removal (decrease in concentration) of a reactant
• following the formation (increase in concentration of product

Question 10

How to measure the progress of a reaction that produces gas?

Answer 10

• monitoring the volume of gas produced at regular time intervals using a gas syringe
• monitoring the loss the loss of mass of the reactant using a balance

Question 11

How to calculate the rate of reaction from mass loss?

Answer 11

1. Plot a graph of mass lost against time
2. Draw a tangent to the curve at concentration
3. Calculate the gradient of the tangent which equals rate

Question 12

What is a catalyst?

Answer 12

A catalyst speeds up the rates if a chemical reaction without being used up or changed (its regenerate). It provides an alternative reaction pathways with a lower activation energy.

Question 13

What’s a homogenous catalyst?

Answer 13

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

Question 14

What is a heterogeneous catalyst?

Answer 14

A heterogeneous catalyst has a different physical state from the reactants.

Question 15

Why are catalysts economically and sustainably important?

Answer 15

Catalyst increase the rate of reaction of most industrial chemicals reactions reducing temperature and energy requirements.
This cuts costs, increasing profitability and using less fossil fuels will cut carbon dioxide emissions.

Question 16

What is the Boltzmann distribution?

Answer 16

The spread of molecule energies in gases. Ea line represents activation energy a thing on the right side of the line has enough energy to react.

Question 17

What are the main features of a Boltzmann distribution?

Answer 17

• no molecules have 0 energy
• areas under the curve is equal to the total number of molecules
• there is no maximum energy of a molecule (line does not touch the x axis)

Question 18

How does temperature affect the Boltzmann distribution?

Answer 18

As the temperature increases, the average energy of molecules also increase so more particles have higher energy making the curve shorter and more stretched out.

Question 19

Why does temperature effect the Boltzmann distribution?

Answer 19

• more molecules have an energy greater than or equal to activation enemy
• therefor a greater proportion of collisions will lead to a reaction increasing rate of reaction
• also the amount of collisions will also increase

Question 20

How does a catalyst affect the Boltzmann distribution?

Answer 20

As a catalyst provides an alternative reaction route with a lower activation energy meaning a greater proportion of molecules will have an energy equal to or greater than Ec (the lowered activation energy) meaning more molecules will react and rate of reaction increases.

Question 21

What are the main features of a dynamic equilibrium?

Answer 21

• the rate if the forward reaction is equal to the rate of the reverse reaction
• the concentrations of reactants and products do not change
• it’s a closed systems meaning temperature, pressure and concentration of reactants are unaffected.

Question 22

What is le Chateliers principle?

Answer 22

When a systems in equilibrium is subjected to an external change the systems will readjust itself to minimise the effect of that change.

Question 23

How does changing the concentration change in the equilibrium?

Answer 23

An increase in concentration of either the reactants or products the equilibrium will shift towards the the side not increasing.
If the concentration of products increase the equilibrium will shift to the left, favouring the backwards reaction and increasing the yield of the reactant. And vis versa

Question 24

How does changing the concentration change in the equilibrium?

Answer 24

An increase in concentration of either the reactants or products the equilibrium will shift towards the the side not increasing.
If the concentration of products increase the equilibrium will shift to the left, favouring the backwards reaction and increasing the yield of the reactant. And vis versa

Question 25

How does changing the concentration change in the equilibrium?

Answer 25

An increase in concentration of either the reactants or products the equilibrium will shift towards the the side not increasing.
If the concentration of products increase the equilibrium will shift to the left, favouring the backwards reaction and increasing the yield of the reactant. And vis versa

Question 26

How does an equilibrium responded to a change in temperature?

Answer 26

• an increase in temperature will shift the equilibrium position in the endothermic direction
• a decrease in temperature will shift the equilibrium positions in the exothermic direction.

Question 27

How does the equilibrium reasoned to changes in pressure?

Answer 27

Increasing the pressure of the system will shift the position of the equilibrium to the side will the fewest molecules of gas, reducing the pressure. And vis versa.

Question 28

How does a catalyst affect an equilibrium?

Answer 28

A catalyst will increase the rate of both the forward and revises reaction resulting in an unchanged position of the equilibrium.
They will speed up the rate at which an equilibrium is formed.

Question 29

How does industry use changes in equilibrium to reduce costs and create higher production?

Answer 29

Le chateliers principle can be used to predict the best conditions of temperature and pressure to force the equilibrium in certain directions to get the highest yield of product.

Question 30

What is Kc and what is its equation?

Answer 30

Kc is the equilibrium constant

Kc = [C]c [D]d
—————
[A]a [B]b
The lower case number ps are the balancing numbers in the overall equation, and are put to the power of the conc of the species.

Question 31

What does Kc tell us?

Answer 31

The magnitude of Kc is used to estimate the position of the equilibrium.
- when Kc = 1 the equilibrium is positioned halfway between the reactants and products.
- If Kc > 1 equilibrium is positioned towards the products
- If Kc < 1 the equilibrium is positioned towards the reactants.