C2.4 - Rates of Reaction

Question 1

What is the “rate of reaction”?

Answer 1

The rate of reaction measures the speed of a reaction or how fast it is.

Question 2

What is an example of a slow reaction?

Answer 2

A slow reaction may be the rusting of iron.

Question 3

What is an example of a moderate speed reaction?

Answer 3

A moderate speed reaction may be a metal reacting with an acid.

Question 4

What is an example of a very fast reaction?

Answer 4

A very fast reaction is an explosion.

Question 5

What is the rate of reaction dependent on?

Answer 5

Temperature

Concentration of solutions

Pressure in gases

Surface area of solids

Catalyst usage

Question 6

What denotes a quick reaction on a graph?

Answer 6

The quickest reaction is shown by the line with the steepest slope.

Question 7

What does it mean if a graph for rate of reaction’s line is high?

Answer 7

If a graph line is higher, then this is because more reactant(s) is added at the start

Question 8

What is the formula for rate of reaction?

Answer 8

Rate of Reaction = amount of reactant used/product formed/Time

Question 9

What is a precipitate rate of reaction experiment?

Answer 9

A precipitate rate of reaction experiment is where the product of the reaction is a precipitate that clouds the solution.

Question 10

How does a precipitate rate of reaction test work?

Answer 10

A precipitate rate of reaction experiment works by observing a mark through the solution and measure how long it takes for it to disappear.

Question 11

The quicker the mark disappears in a precipitate experiment…

Answer 11

The quicker the mark disappears in a precipitate experiment, the quicker the reaction.

Question 12

What are the problems with a precipitate rate of reaction experiment?

Answer 12

However, a precipitate rate of reaction experiment only works for reactions where the initial solution is see-through and the result is dependent on when the person looking notes when the mark is no longer visible.

Question 13

What can a mass balance do?

Answer 13

A mass balance can measure the speed of a reaction that produces a gas.

As the gas is released, the mass disappearing is measured on the balance.

Question 14

The quicker the reading on the balance drops…

Answer 14

The quicker the reading on the balance drops, the faster the reaction.

Question 15

What are the positives of a change in mass rate of reaction experiment?

Answer 15

Graphs are easy to plot with this method and the mass balance is very accurate.

Question 16

What is the negative of a change in mass rate of reaction experiment?

Answer 16

It releases the gas straight into the room.

Question 17

What is the “volume of gas given off” rate of reaction experiment?

Answer 17

A volume of gas given off rate of reaction experiment is where a gas syringe is used to measure the volume of gas given off.

Question 18

“The more gas given off in a given time interval…”

Answer 18

The more gas given off in a given time interval, the faster the reaction.

Question 19

What is a positive and negative of a “volume of gas given off” rate of reaction experiment?

Answer 19

Gas syringes give volumes accurate to the nearest millmitre, hence they are quite accurate, but a too vigorous reaction may lead to the plunger blowing off!

Question 20

What is the method for a marble chip rate of reaction experiment?

Answer 20

Measure the volume of gas given off with a gas syringe and take readings at regular intervals.

Make a table of readings and plot them as a graph - the time is the x axis and the volume is on the y-axis.

Repeat the experiment with same variables but increase the surface area of the marble chips and subsequently repeat using powdered chalk.

Question 21

What is the conclusion of the marble chip rate of reaction experiment?

Answer 21

Increasing the mass or surface area increases the rate of reaction as the collisions are more frequent.

Question 22

What is a magnesium and hydrochloric acid rate of reaction experiment good for?

Answer 22

A magnesium and hydrochloric acid rate of reaction experiment is good for measuring the effects of increased concentration.

Question 23

How can the product of a magnesium-metal rate of reaction experiment be measured?

Answer 23

The reaction gives off hydrogen gas, which we can measure with a mass balance.

Question 24

What are the variables for a graph for the magnesium-metal rate of reaction experiment and how would this be done?

Answer 24

Time goes on the x-axis and volume goes on the y-axis.

The readings of mass would be taken at regular time intervals and the results would be put in a table for the loss in mass for each reading, then a graph would be plotted.

Question 25

What do sodium thiosulfate and HCL have in common? What do they form?

Answer 25

Sodium thiosulfate and HCL are both clear solutions.

They react together to form a yellow sulfur precipitate.

Question 26

What does a sodium thiosulfate and HCl rate of reaction experiment involve?

Answer 26

The experiment involves watching a black mark disappear through the cloudy sulfur and timing how long this takes to occur.

Question 27

How is the temperature in a sodium thiosulfate and HCl rate of reaction experiment changed?

Answer 27

The reaction can be repeated at different temperatures by safely using a water bath.

Question 28

What do the results of a sodium thiosulfate and HCl rate of reaction experiment show?

Answer 28

The results of a sodium thiosulfate and HCl rate of reaction experiment show that the higher the temperature the quicker the reaction and therefore the less time it takes for the mark to disappear.

Question 29

What is the equation for the decomposition of hydrogen peroxide?

Answer 29

2H2O (aq) + 2H2O (l) + O2(g)

Question 30

How can the decomposition of hydrogen peroxide be increased?

Answer 30

The decomposition of hydrogen peroxide can be increased with a manganese(IV) oxide catalyst, or potato peels or blood.

Question 31

What gas is given off in the decomposition of hydrogen peroxide?

Answer 31

Oxygen gas is given off, and this can be used as a means to measure the rate of reaction using a gas syringe.

Question 32

What is the collision theory?

Answer 32

The collision theory states that reactions can only happen if particles collide, and with enough energy to change into new substances. This is known as activation energy.

Question 33

What is the effect of increasing temperature on the rate of reaction?

Answer 33

Increasing the temperature increased the kinetic energy of the particles, so the particles collide more frequently. The particles’ increased energy means more of the collisions are of the right activation energy, hence the rate of reaction increases.

Question 34

What is the effect of increasing pressure on the rate of reaction?

Answer 34

In a gas, increasing the pressure puts more particles into the same volume and reduces the space the particles have to collide in, so there will be more frequent collisions and the rate of reaction increases

Question 35

What is the effect of increasing concentration on the rate of reaction?

Answer 35

In a solution, increasing the concentration means that there are more reactant particles colliding, making collisions more likely and increasing the rate of reaction.

Question 36

What is the effect of increasing surface area on the rate of reaction?

Answer 36

Increasing the surface area increases the area that the particles have to work on, so the frequency of collisions will increase. The rate of reaction increases.

Question 37

What is a catalyst?

Answer 37

A solid catalyst gives the reacting particles a surface to stick to, increasing the number of successful collisions and the rate of reaction.

It is a substance which speeds up a reaction without being changed or used up.

Question 38

How else do catalysts increase the rate of reaction?

Answer 38

Catalysts may also lower the activation energy, so less energy is needed.

Question 39

What are the advantages of catalysts?

Answer 39

They increase the rate of reaction, which means the reaction is quicker and requires less energy.

They reduce the activation energy and reduce the energy used up, saving money and fuel.

They are never used up.

They are only required in small amounts.

Question 40

What are the disadvantages of catalysts?

Answer 40

They are expensive.

They often need to be cleaned.

You need to use a different catalyst for every reaction.

They can be ruined by impurities.

The use of transition metals in catalysts can lead to toxic chemicals being used and environmental damage may occur.