Topic 6 - The Rate And Extent of chemical change

Question 1

How can you find the rate of a chemical reaction?

Answer 1

By measuring the quantity of a reactant used or the quantity of product formed over time

Question 2

What factors affect the rates of chemical reactions?

Answer 2

• Concentrations of reactants in solution
• Pressure of reacting gases
• Service area of solid reactants
• Temperature
• Presence of catalysts

Question 3

How does increasing the temperature increase the rate of reactions?

Answer 3

The particles move faster and collide more frequently so there is more energy

Question 4

How does increasing the concentration increase the rate of reactions?

Answer 4

If the solution is more concentrated there are more particles in the same volume so collisions are more frequent

Question 5

How does increasing pressure increase the rate of reactions?

Answer 5

The same number particles occupy a smaller space so collisions happen more frequently

Question 6

How does increasing the surface area increase the rate of reactions?

Answer 6

For the same volume of the solid the particles around it will have more area to work on so there will be more collisions

Question 7

How does using a catalyst increase the rate of reactions?

Answer 7

A catalyst is a substance that speeds up a reaction without being used up in the reaction its self

Question 8

How do you catalysts work?

Answer 8

They decrease the activation energy needed for the reaction to occur by providing an alternative reaction pathway with a lower activation energy

Question 9

What does collision theory explain?

Answer 9

How various factors affect rates of reactions

Question 10

What is the collision theory?

Answer 10

Chemical reactions can only occur when reacting particles collide with each other and with sufficient energy

Question 11

What is activation energy?

Answer 11

The minimum amount of energy that particles must have to react

Question 12

What increases the frequency of collisions?

Answer 12

• The concentration of reactants in solution
• The pressure of reacting gases
• The surface area of solid reactants

Question 13

How do you increase the energy of collisions?

Answer 13

Increase the temperature

Question 14

Do all reactions need the same catalysts?

Answer 14

No, different reactions need different catalysts

Question 15

Give an example of a biological catalyst?

Answer 15

Enzymes

Question 16

What are reversible reactions?

Answer 16

In some chemical reactions the products of the reaction can react to produce the original reactants

Question 17

How can you change direction of reversible reactions?

Answer 17

By changing the conditions for example heating and cooling

Question 18

If a reversible reaction is exothermic in One Direction what happens in the opposite direction?

Answer 18

It is endothermic but the same amount of energy is transferred in each case

Question 19

What is equilibrium?

Answer 19

When the forward and reverse reactions occur at exactly the same rate

Question 20

When does equilibrium occur?

Answer 20

When a reversible reaction occurs in apparatus which prevent the escape of reactants and products

Question 21

What do the relative amounts of all the reactants and products at equilibrium depend on?

Answer 21

The conditions of the reaction

Question 22

What happens if a system is at equilibrium and a change is made to any of the conditions?

Answer 22

The system responds to counteract the change

Question 23

How can we predict the effects of changing conditions on the system at equilibrium?

Answer 23

Using Le Chatelier’s principle

Question 24

What is Le chatelier’s principle?

Answer 24

The idea that if you change the conditions of a reversible reaction at equilibrium the system will try to counteract that change

Question 25

What happens if the concentration of one of the reactants or products is changed during equilibrium?

Answer 25

The system is no longer at equilibrium and the concentrations of all the substances will change until equilibrium is reached again

Question 26

What happens if the concentration of reactants is increased?

Answer 26

More products will be formed until equilibrium is reached again

Question 27

What happens if the concentration of a product is decreased?

Answer 27

More reactants will react until equilibrium is reached again

Question 28

What happens if the temperature of a system at equilibrium is increased for an endothermic reaction?

Answer 28

The relative amount of products at equilibrium increases

Question 29

What happens if the temperature of the system at equilibrium is increased for an exothermic reaction?

Answer 29

The relative amount of products at equilibrium decreases

Question 30

What happens if the temperature of the system at equilibrium is decreased for an endothermic reaction?

Answer 30

The relative amount of products at equilibrium decreases

Question 31

What happens if the temperature of the system at equilibrium is decreased for an exothermic reaction?

Answer 31

The relative amount of products at equilibrium increases

Question 32

What does an increase in pressure for gaseous reactions at equilibrium cause?

Answer 32

The equilibrium position will shift towards the side with the smaller number of molecules as shown by the symbol equation for that reaction

Question 33

What does a decrease in pressure for gaseous reactions at equilibrium cause?

Answer 33

Equilibrium position will shift towards the side with the larger number of molecules as shown by the symbol equation for that reaction