Rate and Extent of Chemical Change

Question 1

What is the rate of reaction?

Answer 1

How quickly a chemical reaction occurs.

Question 2

What is rusting?

Answer 2

A chemical reaction where iron reacts with oxygen to form iron oxide. This happens very slowly.

Question 3

Do alkali metals and water react at a slow or fast rate?

Answer 3

A very high rate! We can describe this as vigorous.

Question 4

How can you calculate a rate of chemical reaction?

Answer 4

Measuring the quantity of a reactant used over time or the quantity of product formed over time.

Question 5

What are the two calculations for measuring rates?

Answer 5

• mean rate of reaction = quantity of reactant used/time taken
• mean rate of reaction = quantity of product formed/time taken

Question 6

What units are used when measuring the quantities of products/reactants?

Answer 6

mass (grams) or volume (cm^3)

Question 7

What units are used when measuring rate of reaction?

Answer 7

g/s or cm^3/s

Question 8

How can a rate of reaction be calculated on a graph?

Answer 8

By finding the gradient; a steeper gradient=a faster rate

Question 9

What is the rate of reaction like on a curved graph?

Answer 9

Initially, the rate is very high but it gradually slows. The rate is different depending on where you look.

Question 10

How do you calculate the rate of reaction on a curved graph?

Answer 10

• You will be asked to give the rate at a given time
• Draw a tangent at that point and calculate the gradient

Question 11

How do reactions occur?

Answer 11

Two particles must collide with a kinetic energy greater than the activation energy.

Question 12

How is a rate of reaction determined?

Answer 12

By how likely it is that particles will successfully collide.

Question 13

How can we increase the rate of reaction?

Answer 13

By making it more likely that there will be a successful collision.

Question 14

How does increasing temperature increase the number of successful collisions?

Answer 14

It gives particles more kinetic energy, which means that particles will collide more often and a higher kinetic energy means it is more likely to surpass the activation energy.

Question 15

What is concentration?

Answer 15

The number of particles in a given volume.

Question 16

What happens if you increase the concentration of a solution?

Answer 16

• You increase the number of particles in the volume of solution
• This means that particles are more likely to collide with eachother
• By increasing concentration of reactants, you increase rate of reaction

Question 17

What happens when you increase the gas pressure of a solution?

Answer 17

• It forces the same number of particles into a smaller volume
• Particles are more likely to collide; therefore successful collisions are also more likely
• This increases rate of reaction

Question 18

What happens when you increase the surface area of a solid?

Answer 18

• A larger proportion of the solid is revealed for particles to collide with
• Higher surface area = higher chance of colliding with another reactant
• This increases the likelihood of successful collision, therefore increasing ROR

Question 19

How do catalysts increase successful collisions between reactant particles?

Answer 19

• They provide a different pathway for the reaction to occur that has a lower activation energy
• This means that a higher proportion of the reactant particles will have energy greater than the activation energy
• This increases successful collisions per second

Question 20

Why are catalysts an important branch of chemistry in commercial terms?

Answer 20

• They increase rate of reaction
• This increases production rate
• This reduces energy costs (cheaper and quicker)

Question 21

How do rates of reaction change over time?

Answer 21

• They don’t produce at a steady rate (start off at certain speed, gets slower and slower until it stops)
• The concentration of reactants decreases overtime as they are being used up
• This reduces frequency of collisions and therefore ROR

Question 22

What do catalysts do?

Answer 22

• They increase the rate of chemical reactions without being used up.
• They provide a different pathway for the reaction that has a lower activation energy

Question 23

What does it mean by catalysts being specific?

Answer 23

• They are specific for each reaction
• For each reaction, you must use a specific catalyst
• This is because it’s shape must be complimentary to the shape of reactants

Question 24

Why are catalysts so important for industry?

Answer 24

• Products can be made quicker, saving time and money
• They reduce the need for higher temperatures, saving fuel and reducing pollution
• They are essential for living cells

Question 25

What is a reversible reaction?

Answer 25

- A reaction where the products could change back into reactants - It is represented by a double-headed arrow

Question 26

What can we observe when heating hydrated copper sulfate?

Answer 26

- Colour change from blue to white - Water evaporates

Question 27

What are the products from heating hydrated copper sulfate?

Answer 27

Anhydrous copper sulfate and water

Question 28

What can we observe from adding water to anhydrous copper sulfate?

Answer 28

Colour change from white to blue.

Question 29

What is the product made by adding water to anhydrous copper sulfate?

Answer 29

Hydrated copper sulfate.

Question 30

What happens if a reversible reaction is sealed in a container?

Answer 30

- It prevents reactants and products from escaping - It will reach equilibrium - There will be no change in concentration for products or reactants

Question 31

What does it mean when a reversible reaction is 'in equilibrium'?

Answer 31

When a forward and reverse reaction is happening at the same rate.

Question 32

What happens if a reversible reaction is exothermic in one direction?

Answer 32

It is endothermic in the other direction.