C2.4 Rates of reaction

Question 1

What are the 4 things that increase the rate of a reaction?

Answer 1

• Increased temperature
• Adding a catalyst
• Increased concentration/pressure
• Surface area of solids

Question 2

What is the ‘activation energy’ of a reaction?

Answer 2

The minimum amount of energy particles must have to react.

Question 3

Chemical reactions only occur when…

Answer 3

…reacting particles collide with each other with sufficient energy.

Question 4

How does increasing temperature increase the rate of reaction?

Answer 4

• It increases the speed of the reacting particles

- So they collide more often and with more energy

Question 5

How does increasing the concentration/pressure of reacting solutions/gases increase the rate of reaction?

Answer 5

• There are more particles of the reactants within a certain area
• Meaning they are more likely to collide, meaning more frequent collisions

Question 6

How does increasing the surface area of solid reactants increase the rate of reaction?

Answer 6

• The particles around the solid reacting with it will have a larger area to collide with
• Meaning there will be more frequent collisions

Question 7

Define a ‘catalyst’.

Answer 7

A substance which increases the speed of a reaction without being used up or changed

Question 8

How does using a catalyst increase the rate of a reaction?

Answer 8

It gives the reacting particles a surface to stick to, increasing the number of successful collisions.

Question 9

What are the advantages of using catalysts in the industry?

Answer 9

• They increase the rate of reaction, meaning a plant doesn’t have to operate as long to produce the same amount of product
• A catalyst will allow a reaction to work at a much lower temperature, this will reduce the amount of energy needed for the same amount of product.
• They are never used up or changed in the reactions so they can be reused

Question 10

What are the disadvantages of using catalysts in the industry?

Answer 10

• They are expensive to buy
• Different reactions need different catalysts which will all have to be bought
• Catalysts stop working easily from impurities, so the reaction environment needs to be kept clean.

Question 11

Name 3 ways to measure the rate of reaction.

Answer 11

• Precipitation
• Change in mass
• The volume of gas given off.

Question 12

How is precipitation used to measure the rate of reaction?

Answer 12

• This is used when the product of a reaction is a precipitate which clouds the solution.
• Observe a mark through the solution and time how long it takes to disappear.
• The quicker the mark disappears, the quicker the reaction.

Question 13

What is a disadvantage in using precipitation to measure the rate of reaction?

Answer 13

It is very subjective - different people might not agree on the exact point the mark disappears at.

Question 14

How is change in mass used to measure the rate of reaction?

Answer 14

• This is used with a reaction that produces gas (usually)
• As the gas is released the mass disappearing is easily measured on a mass balance.
• The quicker the reading on the balance drops, the faster the rate of reaction.

Question 15

How is the volume of gas given off used to measure the rate of reaction?

Answer 15

• A gas syringe is used to measure the volume of gas given off.
• The more gas given off during a given time interval, the faster the rate of the reaction.

Question 16

What is the unit of concentration in solutions?

Answer 16

mol/dm3 (cubed)

Question 17

When do gases have the same number of molecules?

Answer 17

When they have equal volumes at the same temperature and pressure.