Rates of reaction

Question 1

What rates can reactions happen at?

Answer 1

Reactions can happen at many different rates (iron is slow at rusting, explosions react quickly)

Question 2

What is the rate of reaction dependent on?

Answer 2

Temperature
Concentration (pressure for gases)
Catalysts
Surface area (size for solids)

Question 3

What is the rate of reaction formula?

Answer 3

Amount of reactant used/formed
Rate = __________________________
Time

Question 4

What does the gradient and what does a flat line indicate on a rate of reaction graph?

Answer 4

• Gradient = speed of reaction

- Flat line = reaction has stopped

Question 5

What is the collision theory?

Answer 5

• More collisions increase the rate of reaction
• Faster collisions increase the rate of reaction
• Higher temperature- particles move faster so collide more often
• Higher concentration (or pressure)- more particles closer together so collide more often
• Larger surface area- more area to collide with so more collisions

Question 6

What are the three ways of measuring rates of reaction?

Answer 6

Precipitation, change in mass and volume of gas

Question 7

How do you measure rate of reaction using precipitation and what is its disadvantage?

Answer 7

• Used when a product is a precipate
• Observe a mark and measure how long it takes to disappear
• Result is subjective to opinion

Question 8

How do you measure rate of reaction using change in mass and what is its disadvantage?

Answer 8

• As gas is released, the mass disappearing is easily measured
• Most accurate due to scales, but poisonous gas may be released

Question 9

How do you measure rate of reaction using volume of gas and what is its disadvantage?

Answer 9

• Use a gas syringe to measure volume of gas given off

- Can be very accurate, but syringe can break if reaction is too violent

Question 10

What is an exothermic reaction, what are some examples and where is it used?

Answer 10

• An exothermic reaction is one that transfers energy to its surroundings, usually as heat, and is shown by a rise in temperature of the surroundings
• Examples include combustion, neutralisation, oxidation
• Used in heat packs, hand warmers and self-heating cans

Question 11

What is an endothermic reaction, what are some examples and where is it used?

Answer 11

• An endothermic reaction is one that takes in energy from the surroundings, usually as heat, and is shown by a fall in temperature of the surroundings
• Examples include thermal decomposition
• Used in cool packs

Question 12

What sort of reactions occur in reversible reactions?

Answer 12

One way is exothermic and one way is endothermic

Question 13

What is a catalyst and how does it work?

Answer 13

• A catalyst is a substance which speeds up a reaction without being changed or used up during the reaction
• Solid catalysts give reacting particles a surface to stick to, which increases the number of successful collisions

Question 14

What are the advantages of catalysts?

Answer 14

• Catalysts save money as they speed up reactions so plants don’t need to operate for as long to produce the same amount of substance
• Allow reactions at much lower temperatures, reducing energy used which helps sustainability
• Can be reused

Question 15

What are the disadvantages of catalysts?

Answer 15

• Can be very expensive
• Different reactions need different catalysts
• If catalysts are ‘poisoned’ by impurities, they will stop working