Lesson video

Hello, I am Mrs. Adcock, and welcome to today's lesson on catalysts and rate.

We are going to be looking at what are catalysts and how do they affect the rate of reaction? Today's lesson outcome is, I can describe what a catalyst does and explain how it affects the rate of reaction in terms of activation energy, and justify its use for a reaction based on experimental results.

Some of the keywords we will be using in today's lesson include catalyst, activation energy, reaction profile, and qualitative data.

Here you can see each of those keywords written in a sentence.

It would be a good idea to pause the video now and read over those sentences.

You might like to make some notes that you can refer back to later in the lesson if needed.

Today's lesson on catalysts and rate is split into three main parts.

First of all, we are going to be looking at catalysts and the effect these have on the rate of reaction.

Then we will move on to look at catalysts and activation energy.

And we will finish today's lesson by looking at the effectiveness of catalysts.

Let's get started on the first part of our lesson, catalysts and rate.

A catalyst is a chemical that increases the rate of a chemical reaction without itself being used up.

The decomposition of hydrogen peroxide to produce water and oxygen has a low rate of reaction.

But we can increase the rate of reaction by adding a catalyst.

Let's have a look.

Here we can see the reaction and a catalyst is being added and this increases the rate of this reaction.

And the catalyst that has been added is manganese four oxide.

If you notice at the beginning, the reaction is occurring but at a very low rate of reaction.

But adding the catalyst increased the rate of the reaction.

Here is another example showing the increase in the rate of reaction on addition of a catalyst to the reaction mixture.

In this reaction, we also have the decomposition of hydrogen peroxide.

This reaction, you may have heard of it before, it's often referred to as elephant's toothpaste.

Here the catalyst is added and the reaction then continues at a faster rate.

The decomposition of hydrogen peroxide occurs slowly until the catalyst potassium iodide is added.

Then the rate of reaction rapidly increases.

Time for your question.

What effect does adding a catalyst have on the rate of reaction? A, the rate of reaction increases.

B, the rate of reaction stays the same.

C, the rate of reaction decreases.

The correct answer is A.

Well done if you chose answer A.

When we add a catalyst, it will increase the rate of reaction.

Catalysts are useful in many different applications.

They are used in catalytic converters to decrease the pollution from cars.

Here we can see the reaction that takes place in a catalytic converter.

Carbon monoxide and nitrogen monoxide react together and they produce carbon dioxide and nitrogen.

This reaction reduces the amount of carbon monoxide and nitrogen monoxide, which are both atmospheric pollutants being released into the atmosphere.

The catalysts rhodium and platinum increase the rate of this reaction without themselves being used up.

And we can see in the image there, we have a catalytic converter, which is where this reaction takes place.

Catalysts are also used in industry to ensure products are made efficiently and in a cost-effective manner.

We can see in the image there that we have an ammonia synthesis chamber.

Now ammonia is a really useful product.

Ammonia is used in fertilisers and it is produced in the Haber process.

Here we can see what happens during that process.

Nitrogen and hydrogen react together to produce ammonia, and you will notice that this is a reversible reaction.

So we have the symbol there for a reversible reaction.

Below the word equation, we have a balanced symbol equation for this reaction.

So two nitrogen molecules react together with three hydrogen molecules to produce two molecules of ammonia, and each of these substances is in the gaseous state.

The rate of this reaction can be increased by adding a catalyst, and we use an iron catalyst to increase the rate of this reaction.

Enzymes are biological catalysts.

The rate of chemical reactions in cells is much higher with enzymes, so with those biological catalysts, than without.

Here in the chart, we can see we have the rate of reaction and we can see the rate of reaction without an enzyme and with an enzyme.

And hopefully you can notice that the rate of reaction is much higher when we have an enzyme, and that's because our enzymes are biological catalysts and catalysts increase the rate of reaction.

Without enzymes, many chemical reactions would not happen quickly enough to keep cells alive.

So these enzymes are essential for life.

Time for your question.

What are enzymes? Are they A, minerals providing nutrients to plants? B, biological catalysts? C, simple sugars providing energy? Or D, lipids that form cell membranes? The correct answer is B, enzymes are biological catalysts.

Well done if you got that question correct.

Time for our first practise task of today's lesson.

The production of ammonia involves reacting nitrogen and hydrogen together in the presence of iron.

We can see the word equation and a balanced symbol equation for this reaction, including state symbols.

Question one.

What is the role of iron in this reaction? Question two.

What effect does adding iron to the reaction have on the production of ammonia? And three.

Explain why the iron does not need to be replaced once the reaction is complete.

Pause the video now, answer all three of these questions, and then when you come back, we will go over the answers.

Question one.

What is the role of iron in this reaction? The iron acts as a catalyst.

What effect does iron have on the rate of ammonia production? The iron catalyst increases the rate of this reaction, so increases the rate at which ammonia is produced.

Question three.

Explain why the iron does not need to be replaced once the reaction is complete.

Catalysts increase the rate of reaction without being used up themselves.

So the iron does not need to be replaced each time the reaction takes place and is completed.

Well done if you got those questions correct.

We have had a look at catalysts and the effect that these have on the rate of reaction.

Now we are going to move on to look at catalysts and activation energy.

For a chemical reaction to take place, particles in the reactants must collide with each other.

And the minimum energy that the particles must have in order to react when they collide is known as the activation energy.

Here we can see that these particles have energy higher than the activation energy.

And when they collide, they are able to react and form a new product.

So we have AB and C.

These react together, they collide with each other, and they have energy higher than or equal to the activation energy.

And therefore when they collide, a reaction takes place and new products are formed.

Our new products are A and BC.

Catalysts provide an alternative pathway with a lower activation energy.

Here we can see a model showing us the particles when we do not have a catalyst present.

The lighter shade shows us the particles with energy lower than the activation energy, and the circles with a darker shade show us particles with at least the activation energy.

So these have the activation energy or higher.

We can see that without a catalyst in this model, most of the particles have energy lower than the activation energy.

So if these collide together, they will not have enough energy to react.

When we add a catalyst, we provide an alternative pathway with a lower activation energy.

So now more of our particles have at least the activation energy.

Now more of these particles when they collide will be able to react and form products.

With a catalyst, more particles have energy higher or equal to the activation energy.

Therefore, more collisions will be successful and result in a reaction.

So this is how a catalyst can increase the rate of a reaction.

Which of the following statements about catalysts are true? A, catalysts provide an alternative pathway for a reaction.

B, catalysts lower the activation energy.

C, when a catalyst is present, less reacting particles have the activation energy.

D, when a catalyst is present, there will be more successful collisions between reactant particles.

Read back over those statements carefully and decide which of the statements you think are true.

The correct answers are A, catalysts provide an alternative pathway.

B is also correct.

They provide an alternative pathway with a lower activation energy.

And D is also correct.

When a catalyst is present, there will be more successful collisions between reactant particles because more of the particles will have energy equal to or greater than the activation energy.

C is not correct, because with a catalyst, more reacting particles will have the activation energy, so there will be more successful collisions and catalysts increase the rate of reaction.

This reaction profile shows the energy of the reactants and products in a chemical reaction.

So we've got the energy on the y-axis.

We've got the reaction time on the x-axis.

And we can see how much energy our reactants have, and that our products have a lower amount of energy.

So you may recognise that this is a reaction profile for an exothermic reaction where energy has been released into the surroundings.

If you notice, from the level of the reactants to the top of our curve, that is the activation energy.

And in this example here, that is the activation energy without a catalyst.

If we add a catalyst, a catalyst will provide an alternative pathway for the reaction with a lower activation energy.

So how can we show that on our reaction profile? Well, here we have a reaction where we have added a catalyst.

The energy level of the reactants and the energy level of the products remains the same, but the activation energy is lower when we have a catalyst present.

Just to summarise, the activation energy is lower for the reaction with a catalyst.

Time for another question.

If you have a look at the reaction profile shown there, the question is, what does the missing label A show? Is it A, the reactant energy level? B, the product energy level? C, the activation energy with a catalyst? Or D, the activation energy without a catalyst? The correct answer is D.

So well done if you chose answer D.

Label A shows the activation energy without a catalyst, and this activation energy would be lower if we used a catalyst.

Time for another practise task.

Sam is investigating the effect of adding a catalyst on the rate of decomposition of hydrogen peroxide.

We have the reaction shown here as a word equation.

So hydrogen peroxide can decompose to produce water and oxygen.

And we have a balanced symbol equation for this reaction where two molecules of hydrogen peroxide will decompose to produce two molecules of water and a molecule of oxygen.

And with that balanced symbol equation, you can see the state symbols are included.

There's also an image showing the apparatus set up for Sam's investigation.

He has the hydrogen peroxide in a conical flask and he has added a catalyst.

And then he is measuring the volume of oxygen gas that is produced in an upturned measuring cylinder.

Question one.

Explain how adding a catalyst to this reaction increases the rate of reaction.

Pause the video now, have a go at answering this question, then when you come back, we will go over the answer.

Let's see how you got on.

Explain how adding a catalyst increases the rate of reaction.

A catalyst provides an alternative pathway for the reaction that has a lower activation energy.

More particles have at least the activation energy, which increases the frequency of successful collisions.

Well done if got that question correct and you had lots of that scientific detail in your answer.

For the second part of this practise task, you need to complete and label the reaction profile to show the energy level of a reaction with and without a catalyst.

Pause the video now and have a go at completing this reaction profile and remember to add labels to your reaction profile.

The reactants were already given for you on the reaction profile, but you needed to complete the profile and label the products.

This curve that we have shown now is without a catalyst, and we can see here we've labelled the activation energy without a catalyst, and this goes from the level of the reactants up to the top of our curve.

And then we've drawn a second curve, which is the reaction taking place with a catalyst.

Now the level of the reactants and the energy level of the products is the same when we used a catalyst and when we didn't have a catalyst present.

But you will notice that our curve does not rise as high, and that's because the activation energy is lower with our catalyst.

So make sure you have labelled an arrow that should go from the level of the reactants up to the top of that curve, and that's the activation energy with a catalyst.

Well done if you have correctly drawn and labelled your reaction profile.

We have looked at how catalysts can increase the rate of reaction without being used up themselves, and we have seen how catalysts do this by providing an alternative pathway with a lower activation energy.

We are now going to move on to the final part of our lesson on the effectiveness of catalysts.

Catalysts are highly specific to particular reactions.

We can use qualitative data to evaluate the effectiveness of a catalyst.

Qualitative data is information that describes qualities or characteristics that cannot be measured using numbers.

Manganese dioxide can be used to catalyse the decomposition of hydrogen peroxide.

We can see in our conical flask that we have hydrogen peroxide and we have added the catalyst manganese dioxide.

When manganese dioxide is in the presence of hydrogen peroxide, a lot of bubbling is observed, and we can see all the bubbles in our conical flask.

When we use copper oxide instead to catalyse the decomposition of hydrogen peroxide, only a few bubbles are formed.

We can see in our conical flask, we have hydrogen peroxide and we have the catalyst copper oxide, and this time, we only have a few bubbles.

We can use this qualitative data to help us analyse the effectiveness of these catalysts.

And manganese dioxide appears to be a more effective catalyst than copper oxide for this reaction.

Time for your question.

Which of the following statements are true? A, all catalysts increase the rate of any chemical reaction.

B, qualitative data helps us evaluate the effectiveness of catalysts.

C, qualitative data enables numerical analysis of catalysts.

Or D, the rate of a reaction can be increased using a specific catalyst for that reaction.

B is correct.

Qualitative data helps us to evaluate the effectiveness of catalysts.

And D is also correct.

The rate of a reaction can be increased using a specific catalyst for that reaction.

A is incorrect, because not all catalysts increase the rate of any chemical reaction.

Catalysts are highly specific for certain reactions.

Time for our final practise task of today's lesson.

Alex is investigating the effect of different catalysts at increasing the rate of decomposition of hydrogen peroxide.

And we have the word equation for this reaction written there.

Hydrogen peroxide will break down.

It will decompose to produce water and oxygen.

We have a results table where Alex has used three different catalysts, manganese dioxide, copper oxide, and zinc oxide.

You can see the observations that Alex made when he added each of those catalysts to hydrogen peroxide.

Question one.

State two control variables used in this investigation.

And question two.

Which is the most effective catalyst for this reaction? Explain your answer.

Pause the video now, have a go at answering these two questions, and then come back when you're ready to go over the answers.

Question one.

State two control variables used in this investigation.

Control variables are variables that we keep constant or the same throughout an investigation.

Your answer may include the concentration of the hydrogen peroxide, the surface area of the catalysts, and temperature.

Well done if you were able to identify two control variables.

Question two.

Which is the most effective catalyst for this reaction? And explain your answer.

The most effective catalyst for this reaction is manganese dioxide.

And this catalyst increased the rate of reaction the most, and we know this because it resulted in rapid bubbling as oxygen gas is produced.

Great work if you got that question correct.

We have reached the end of today's lesson on catalysts and rate.

Let's just summarise some of the key points that we have covered in today's lesson.

A catalyst affects the reaction rate without being used up.

And we've seen how a catalyst will increase the rate of reaction.

A catalyst reduces the activation energy needed for a reaction by providing an alternative pathway with a lower activation energy.

With a catalyst present, more collisions between reactants result in the formation of product or products.

Enzymes are biological catalysts.

And catalysts vary in efficiency, and we can use qualitative data to help us evaluate the effectiveness of catalysts.

Well done for your great work in today's lesson! I've really enjoyed the lesson and I hope you have too, and I hope you're able to join me for another lesson soon.