Section 14 - Rates Of Reaction

Question 1

What are always formed in chemical reactions?

Answer 1

New substances

Question 2

What is a rate of reaction?

Answer 2

The speed at which reactants turn to products

Question 3

How do rates vary?

Answer 3

From very slowly to almost instantaneously

Question 4

How can we control rates of reaction?

Answer 4

By altering variables

Question 5

What are the main variables to change when controlling the rate of reactions?

Answer 5

Concentration of solution / size of pieces of solid reactant

Question 6

What do we need to be able to investigate reaction rates?

Answer 6

To be able to measure how the amount of reactants or products change with time

Question 7

What does the gradient in a reactant graph show?

Answer 7

It indicates the rate: faster= steeper

Question 8

When are section rates usually faster and why?

Answer 8

At the start because that’s when the concentration of reactants is greatest

Question 9

How can we monitor rates?

Answer 9

By measuring changes in the mass or volume of reactants or products

Question 10

What reactants with sulfuric acid quicker: magnesium granules or ribbon?

Answer 10

Granules, because they’re smaller pieces and have a larger surface area

Question 11

How do you measure the volume of hydrogen gas produced (from magnesium in sulfuric acid)

Answer 11

Put the magnesium in a conical flask containing dilute sulfuric acid and seal it with a gas syringe attached to measure the hydrogen

Question 12

How do you measure the change in mass in a reaction (between magnesium and sulfuric acid)?

Answer 12

Put the magnesium in dilute sulfuric acid in a conical flask and add cotton wool at the top to stop acid spray escaping - place on a scale and the contents should decrease

Question 13

What must happen for chemical reactions to occur?

Answer 13

Reactant particles must bump together with enough energy to react

Question 14

What is the minimum amount of energy needed for a reaction to occur called?

Answer 14

Activation energy

Question 15

What does activation energy do during successful collisions?

Answer 15

Helps to break bonds, so atoms can rearrange to make new substances

Question 16

What is needed for methane and air to react?

Answer 16

A spark to provide activation energy (it won’t react if they’re just mixed in the air and the molecules collide)

Question 17

What are reactions that release energy called?

Answer 17

Exothermic

Question 18

What is the type of reaction which energy for the surroundings is transferred to the products?

Answer 18

Endothermic

Question 19

What happens to reaction rates when the energy collision and frequency is increased?

Answer 19

The reaction rate increases (gets faster)

Question 20

If particles are further apart will more or less reactions take place?

Answer 20

Less reactions

Question 21

Do all particles in a substance have energy?

Answer 21

Yes they have a range of energies but only those with enough energy can react

Question 22

What 4 things increase reaction rate?

Answer 22

Concentration / surface area / pressure of gases / temperature

Question 23

How and why does concentration affect the rate of reaction?

Answer 23

Increasing the concentration increases the rate — there are more reactant particles in the same volume so collisions occur more often

Question 24

How and why does surface area affect the rate of reaction?

Answer 24

Increasing surface area to volume ratio, by decreasing the size of solid pieces while keeping the volume the same, it increases the rate of reaction — there is more surface for collisions to occur on, so collisions occur more often

Question 25

How and why does the pressure of gases increase the rate of reaction?

Answer 25

Increasing the pressure increases the rate - reactant particles are squeezed closer together so collisions occur more often

Question 26

How does temperature affect the rate of reaction?

Answer 26

Increasing temp increases rate of reaction — reactant particles speed up and have more energy when heated, so therefore collide more often and more particles with have enough energy to react when they collide

Question 27

What are catalysts?

Answer 27

Substances that speed up chemical reactions without permanently changing themselves and without altering the products of the reaction

Question 28

If you ass 1g of manganese dioxide to catalyse a reaction, how much will you have at the end?

Answer 28

1g because the catalyst is not used up

Question 29

How are catalysts useful in industries?

Answer 29

They can make industrial processes more profitable by making products quicker / allowing reactions to occur at lower temperatures, saves costs / catalysts don’t need to be replaced as they’re not used up

Question 30

What do catalysts offer which requires less activation energy?

Answer 30

An alternative reaction route

Question 31

What is a reaction profile?

Answer 31

A graph to show the energy changes for a catalysed and an uncatalysed exothermic reaction

Question 32

Why are collisions more successful with catalysts?

Answer 32

As less energy is needed to start the reaction, more reactant molecules have enough energy and so more collisions are successful (as more particles have energy than rise that would be sued in the beginning)

Question 33

What does the presence of platinum and palladium in car exhausts do?

Answer 33

Lower the activation energy needed to convert harmful gases to harmless gases

Question 34

What are enzymes and what do they act as?

Answer 34

They’re large complex protein molecules that act as catalysts in biological reactions