C8

Question 1

What does rate of reaction mean?

Answer 1

The rate of a chemical reaction is how fast the reactants are changed into products

Question 2

Give an example of a moderate speed reaction

Answer 2

Metal magnesium reacting with an acid to produce a gentle stream of bubbles

Question 3

What is turbidity?

Answer 3

How cloudy the precipitate is

Question 4

The steeper the line on a rate of reaction graph…

Answer 4

The faster the rate of reaction

Question 5

Why does the line become less steep over time on a rate of reaction graph?

Answer 5

Because the reactants are used up

Question 6

What do the quickest reactions have in the rate of reaction graphs?

Answer 6

The quickest reactions have the steepest lines and become flat in the least time.

Question 7

What is collision theory? And when are reactions more likely to happen ?

Answer 7

-Particles must collide with enough energy in order to react

So reactions are more likely to happen between reactant particles if you:
- Increase the frequency of reacting particles colliding with each other
- Increase the energy they have when they collide

If you increase the chance of the particles reacting, you are increasing the rate of reaction

Question 8

What is activation energy?

Answer 8

It is the minimum amount of energy that particles need to react

Question 9

What are the 4 things that the rate of reaction depends on? And what do all these increase?

Answer 9

-Temperature
-The concentration of the solution or the pressure of the gas
-Surface area
-The presence if a catalyst

All these increase the rate of reaction by increasing the number of succesful collisions between reacting particles

Question 10

How does increasing the temperature increase the Rate of reaction?

Answer 10

When the temperature is increased, the particles all move faster.

If they’re moving faster, they’re going to collide more frequently.

Also the faster they move the more energy they have, so more of the collisions will have enough energy to make the reaction happen.

Question 11

How does increasing the concentration or pressure increase the rate of reaction?

Answer 11

If a solution is made more concentrated, it means there are more particles knocking about in the same volume of water (or other solvent).

Similary, when the pressure of the gas is increased, it means that the same amount of particles occupies a smaller space

This makes the collisions between the particles more frequent

Question 12

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

Answer 12

If one of the reactants is a solid, then breaking it up into smaller pieces will increase its surface area to volume ratio.

This means that for the same volume of the solid, the particles around it will have more area to work on - so there will be collisions more frequently.

Question 13

How does using a catalyst increase the rate of reaction?

Answer 13

A catalyst is a substance that speeds up a reaction, without being used up in the reaction itself. This means it’s not part of the overall reaction equation.

Different catalysts are needed for different reactions, but they all work by decreasing the activation energy needed for the reaction to occur.

They do this by providing an alternative reaction pathway with a lower activation energy.

Question 14

What are enzymes?

Answer 14

They are biological catalysts that catalyse reactions in living things

Question 15

What are the advantages of catalysts in industry?

Answer 15

Catalysts are used whenever possible in industry to increase rates of reaction and reduce energy costs.

So catalysts save money and help the environment. That is because using high temperatures and pressures often involves burning fossil fuels. So operating at lower temperatures and pressures conserves these non-renewable resources. It also stops more carbon dioxide entering the atmosphere when they are burnt, helping to combat climate change.

Question 16

Mean rate of reaction formula

Answer 16

Rate of reaction = Amount of reactant used up or amount of product formed / Time

Question 17

What are the 3 main ways of measuring the rate of reaction?

Answer 17

PRECIPITATION AND COLOUR CHANGE:
1) You can record the visual change in a reaction if the initial solution is transparent and the product is a precipitate which clouds the solution (it becomes opaque).

2) You can observe a mark through the solution and measure how long it takes for it to disappear -
- the faster the mark disappears, the quicker the reaction.

3) If the reactants are coloured and the products are colourless (or vice versa), you can time how long it takes for the solution to lose (or gain) its colour.

4) The results are very subjective - different people might not agree over the exact point when the mark ‘disappears’ or the solution changes colour.

CHANGE IN MASS (usually gas given off):
1) Measuring the speed of a reaction that produces a gas can be carried out using a mass balance.
2) As the gas is released, the mass disappearing is measured on the balance.
3) The guicker the reading on the balance drops, the faster the reaction.
4) If you take measurements at regular intervals, you can plot a rate of reaction graph and find the rate quite easily

THE VOLUME OF GAS GIVEN OFF:
1) This involves the use of a gas suringe to measure the volume of gas given off.
2) The more gas given off during a given time interval, the faster the reaction.
3) Gas syringes usually give volumes accurate to the nearest cm°, so they’re quite accurate. You can take measurements at regular intervals and plot a rate of reaction graph using this method too.
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You have to be quite careful though if the reaction is too vigorous, you can easily blow the plunger out of the end of the syringe.

Question 18

How do you do the Magnesium and HCL reaction that produces H2 gas?
Effect of concentration on the rate of reaction RP
What does the cotton wool do in the experiment?

Answer 18

1) Start by adding a set volume of dilute hydrochloric acid to a conical flask and carefully place on a mass balance.

2) Now add some magnesium ribbon to the acid and quickly plug the flask with cotton wool.

3) Start the stopwatch and record the mass on the balance. Take readings of the mass at regular intervals.

4) Plot the resulfs in a table and work out the mass lost for each reading. Now you can plot a graph with time on the ×-axis and loss of mass on the y-axis.

5) Repeat with more concentrated acid solutions. Variables such as the amount of magnesium ribbon and the volume of acid used should be kept the same each time - only change the acid’s concentration. This is to make your experiment a fair test

6) The three graphs show that a higher concentration of acid gives a faster rate of reaction.

You could also do this experiment by measuring the gas released using a gas syringe

The cotton wool at the top of the flask lets the gas escape but stops the acid from spitting out

Question 19

How to do the Sodium Thiosulfate and HCI Produce a Cloudy Precipitate practical?
Or What is the effect of concentration on the rate of reaction?

Answer 19

1) These two chemicals are both clear solutions. They react together to form a yellow precipitate of sulfur

2) Start by adding a set volume of dilute sodium thiosulfate to a conical flask.

3) Place the flask on a piece of paper with a black cross drawn on it.
Add some dilute HCI to the flask and start the stopwatch.

4) Now watch the black cross disappear through the cloudy sulfur and time how long it takes to go

5) The reaction can be repeated with solutions of either reactant at different concentrations. (Only change the concentration of one reactant at a time though). The depth of the liquid must be kept the same each time.

6) The higher the concentration, the quicker the reaction and therefore the less time it takes for the mark to disappear.

Question 20

What is a reversible reaction?

Answer 20

The products of the reaction can react to make the original reactants

Question 21

Give an example of a reversible reaction

Answer 21

CuSO4.5H20 =reversible reaction symbol CuSO4 + 5H2O

Question 22

In reversible reactions, if the reaction is exothermic one way then it will be

Answer 22

Endothermic the other way

Question 23

What does anhydrous and hydrated mean?

Answer 23

Anhydrous means without water ( dry )
Hydrated means with water

Question 24

In reversible reactions, the amount of energy transferred from the surroundings by the endothermic reaction is equal to….

Answer 24

The energy transferred to the surroundings during the exothermic reaction

Question 25

When a reaction is at equilibrium it doesn’t mean the amounts of reactants and products are ….

Answer 25

Equal

Question 26

What is Le chateliers principle?

Answer 26

Le chateliers principle is the idea that if you change the conditions of a reversible reactions ( so either conc, pressure, temp ) at equilibrium, the system will try to counteract that change

Question 27

What happens when the equilibrium shifts to one side

Answer 27

More of the shifted side gets made