Rates of Reaction

Question 1

What are the four main contributing factors to the rate of a reaction?

Answer 1

• Temperature
• Concentration/pressure
• Surface area to volume ratio
• Action of catalysts

Question 2

Using collision theory, what are the two ways of increasing the rate of reaction?

Answer 2

• Increase the number of collisions so that the number of successful collisions increases
• Increase the energy of the collisions

Question 3

Using collision theory, explain the effect of temperature increase on the rate of reaction.

Answer 3

When the temperature is increased, the particles gain energy and move quicker. Because they are moving quicker they collide more often. Also, the particles having more energy means it’s more likely for the particles to collide with enough energy for a reaction to take place.

Question 4

Using collision theory, explain the effect of increasing the concentration or pressure on the rate of reaction.

Answer 4

If a solution is more concentrated or a gas is under a higher pressure, there will be more particles in a smaller space so collisions are more likely.

Question 5

Using collision theory, explain the effect of increasing the surface area of the reactant on the rate of reaction.

Answer 5

If the surface area is increased, the particles will have a larger area to work on so collisions will be a lot more frequent.

Question 6

What is activation energy?

Answer 6

The minimum amount of energy that particles in a reaction must have in order to react.

Question 7

What is a catalyst?

Answer 7

A substance which can speed up a reaction without being changed or used up. It does this by opening up alternative reaction pathways that require less energy, so the activation energy decreases.

Question 8

What are two advantages of using catalysts in industry?

Answer 8

• They can be used over and over again

* Less energy is required for a reaction which keeps costs down

Question 9

What are three disadvantages of using catalysts in industry?

Answer 9

• They can be expensive and can require cleansing before use
• Catalysts only work on specific reactions
• Catalysts can stop working if they are mixed with some impurities

Question 10

How do you work out the rate of reaction?

Answer 10

Amount of product formed or reactant used / time

Question 11

What are three ways of measuring the rate of reaction?

Answer 11

• If the reaction is a precipitate reaction, time how long it takes for a mark to disappear
• Measure the change in mass of the reaction over time
• Measure the volume of gas produced over time using a gas syringe

Question 12

What is an advantage and a disadvantage of using the precipitate method of measuring rate of reaction?

Answer 12

+Very easy

-Very subjective

Question 13

What is an advantage and a disadvantage of using change in mass to measure the rate of reaction?

Answer 13

+Tge mass balance is very accurate

-Gas has to be released into the room which can be very dangerous

Question 14

What is an adavtabge and a disadvantage of using the volume of gas produced to measure the rate of reaction?

Answer 14

+Gas syringes are very accurate and prevent the gas escaping

-A vigorous reaction could blow the plunger out of the syringe

Question 15

On a date of reaction graph, what should the x- and y-axes be labelled?

Answer 15

X should be time

Y should be amount of product formed

Question 16

What does the gradient of the line on a rate of reaction graph tell us?

Answer 16

The rate of reaction. The steeper the line, the faster the rate.

Question 17

Why do reactions start quickly but slow down over time?

Answer 17

At the beginning of the reaction there are lots of reactant particles around so collisions are very frequent. As the reactants get used up, the collisions become less and less frequent so the rate of reaction slows down.

Question 18

How can one use a rate of reaction graph to compare reactions?

Answer 18

• The fastest reaction will have the steepest gradient
• The earlier the line becomes flat, the quicker it finished
• Lines that level off at similar points will have the same amount of reactants

Question 19

What experiment can be used to show the effect of surface area on the rate of reaction?

Answer 19

The mixing of hydrochloric acid and marble chips.

Question 20

What is the equation for the reaction between hydrochloric acid and marble chips?

Answer 20

2HCl(aq) + CaCO3(s) -> CaCl2(aq) + H2O(l) + CO2(g)

Question 21

How does one measure the rate of reaction during the reaction between hydrochloric acid and marble chips?

Answer 21

By using a gas syringe to measure the amount of carbon dioxide produced.

Question 22

How do you change the reaction between hydrochloric acid and marble to show the effect of surface area?

Answer 22

You measure the volume of gas with a gas syringe at regular intervals. Then you repeat the experiment with smaller chips of the same total mass and repeat, and then perform a third time with a powdered chalk.

Question 23

What reaction would you use to exhibit the effect of concentration on the rate of reaction?

Answer 23

Magnesium metal and hydrochloric acid

Question 24

What is the equation for the reaction between magnesium and hydrochloric acid?

Answer 24

2HCl(aq) + Mg(s) -> MgCl2(aq) + H2(g)

Question 25

How do you measure the rate of reaction between magnesium and hydrochloric acid?

Answer 25

Using a mass balance

Question 26

How can you use the reaction between magnesium and hydrochloric acid to show the effect of concentration on the rate of reaction?

Answer 26

1) Take mass readings at regular intervals
2) Plot the results
3) Repeat the experiment with increasingly more concentrated acid solutions but with the same amount of magnesium.

Question 27

What reaction can we use to show the effect of temperature on the rate of reaction?

Answer 27

Sodium thiosulphate and hydrochloric acid

Question 28

What is the equation for the reaction between sodium thiosulphate and hydrochloric acid?

Answer 28

2HCl(aq) + Na2S2O3(aq) -> 2NaCl(aq) + SO2(g) + S(s) + H2O(l)

Question 29

How does one measure the rate of reaction between sodium thiosulphate and hydrochloric acid?

Answer 29

By drawing a black mark under the flask and timing how long it takes the mark to disappear.

Question 30

How does one use the reaction between sodium thiosulphate and hydrochloric acid to show the effect of temperature on rate of reaction?

Answer 30

You place flasks of the reactants in water baths and heat them to different temperatures. Record how long it takes each one’s mark to disappear. Compare the timings.

Question 31

What is a good reaction to show the effect of catalysts on rate of reaction?

Answer 31

The decomposition of hydrogen peroxide.

Question 32

What is the equation for the decomposition of hydrogen peroxide?

Answer 32

2H2O2(aq) -> 2H2O(l) + O2(g)

Question 33

How do you measure the rate of reaction during the decomposition of hydrogen peroxide?

Answer 33

By using a gas syringe

Question 34

What are three catalysts that can be used during the decomposition of hydrogen peroxide?

Answer 34

•Manganese (IV) Oxide, potato peel and blood.